No legal duty to save someone in distress
In Hong Kong, there is generally no legal duty to save someone in distress. Liability for a failure to act will only arise when a legal duty to act is recognized. Examples are quoted as follows.
the parties concerned have special relationship that creates duty of care among them, for example, between parents and child  ;
the person concerned is the one who creates harmful situation  ;
the person is under a contractual duty to save, for example lifeguards  who are on duty;
the person has voluntarily undertaken the care of another  ; or
the duty to act is explicitly specified in statue, for example, a woman should not wilfully omit her infant to avoid causing the death of her child 
This doctrine is established because it is believed that coercive powers of law should only be invoked in response to positive actions, or else law would become overly burdensome and intrusive to individual freedom. Also, liability for omissions entails the possibility of numerous liabilities wherever there is no particular reason for attributing responsibility to one rather than another person. Moreover, most of the failure to act is not that serious to the extent that criminalisation is needed.
In some countries like France which is practicing civil law system, however, it is stipulated that one shall be punished by imprisonment if someone “abstains voluntarily from giving such aid to a person in peril that he would have been able to give him without risk to himself or to third persons by his personal action or by calling for help".  Germany in law system there is a provision that also specifies “a citizen is obliged to provide help in case of accident or general danger if necessary". 
In my opinion, common law is not too lenient, and I am in support of the current law in Hong Kong that a person should only be criminally liable if there is a duty of care involved. As said by legal scholar Glanville Williams, “the word crime is expressed with the implications of action, it is a breach of the principle of legality to convict people of them when they have not acted; and it is unfair to convict non-doers of acts under the names of doers"  . If we follow Germany’s practice, people would help out of the fear of being prosecuted. The law then takes on the role of forcing people to act instead of prohibiting undesirable acts, and this would be intrusive to one of mankind’s greatest value, freewill.
It is worth to mention that, In US and Canada, although there is no general duty to save, there is Good Samaritan (GS) Laws.  GS Laws aims to protect those who choose to aid others who are in distress from liable for damages that result from the person’s negligence in acting or failing to act while providing the services, unless it is established that the damages were caused by the gross negligence of the person. There are no laws serve the purpose of GS Laws in Hong Kong right now. By diminishing the liability, it may encourage people to assist the ones who are in distress, and provides an alternative solution apart from criminalizing the duty to save.
By the same token, should the common law demand more of people who are involved in a criminal joint enterprise and wish to withdraw from the enterprise?
It is known that a person may avoid liability where he has been an active member of the joint enterprise by withdrawal before the others go on to commit the crime. Several factors will be taken into account when the court is considering whether the withdrawal is acceptable. Below lists out two of the major factors supported by cases.
Nearness to the completion of offence
R v Whitefield
W has successfully pleaded that he had withdrawn from the common enterprise to burgle the adjoining flat, by informing the principal that he did not wish to take part in it, and by refusing to allow him access to his flat and balcony for the purpose of effecting entry to his neighbour's flat.
R v Becerra
B had given C a knife to use in case there was any trouble. When they were disturbed by one of the tenants, B jumped out of the window and ran off, shouting "There's a bloke coming. Let's go." C remained behind and murdered the tenant. B was then convicted of murder as a joint enterprise. Judge Roskill LJ stated that “if B wanted to withdraw at that stage he would have to "repent" in some manner vastly different and vastly more effective than merely to say "Come on, let's go" and go out through the window".
Spontaneous and planned offences
A defendant may be able to withdraw from participation if he gives “timely and unequivocal" notice to others that he is not going to be involved. There is less time to communicate withdrawal if an offence occurs spontaneously, and the qualifying bar for withdrawal will be lowered in such case.
R v Mitchell
In this non-planned spontaneous violence, the defendant threw down his weapon and walked away. His action was considered as a sufficient withdrawal.
R v Robinson
In this non-spontaneous violence case, where the defendant has encouraged the commission of an offence and struck the first blow but ultimately intervening to protect victim, it is shown that he has in fact wilfully encouraged the commission of the offence, then by the time he has given his encouragement he has played his part and thereafter he cannot escape liability by attempting to withdraw at that stage.
The joint enterprise doctrine is built to ensure that liability can be attached to secondary party when (a) the principle offender cannot be identified (like in group attack); (b) the offender withdraws from the offence at the last moment in hope to escape liability, or (c) one of the participant commits a different offence, usually more serious than that intended by the parties when set out in their enterprise. In my opinion, the common law’s requirement of a withdrawal from a joint enterprise is reasonable. It is a fair approach that forces people to take on the responsibility for their own conduct. Requiring more of that would be unjust and discouraging to the party who wishes to withdraw.
Should someone who is aware that an arrestable offence has taken place be under a positive duty to tell the authorities of the offence?
Generally speaking, in common law jurisdiction, there is no positive duty to tell the authorities of the offence, unless otherwise stated in the statue. In Hong Kong, it is stated in the ordinance that a person knows or suspects that any property is intended to be used, or in connection with, organized and serious crime  , drug trafficking  or terrorism  , shall as soon as possible disclose that knowledge or suspicion to an authorized officer. Contravening such will be liable to fine and imprisonment.
Some civil law jurisdictions like France implement a far higher requirement on the duty to report crime than common law jurisdictions. In accordance with French Penal Code  , any person who, having knowledge of any serious criminal offence of which it is still possible to prevent or limit, omits to inform the authorities is punishable by imprisonment and fine. Germany adopts a similar approach in this aspect as well.
Indeed, if an offence is prevented, its intended victim will not suffer the harm it would have caused. In this situation a duty to report will not only benefit a particular individual but also the community as a whole. However, if every offence is to be reported, attention may than be distracted from serious offences to less serious and easily discoverable offences. Moreover, it will give an excuse for malicious reporting.
The question of whether a person should be compelled by the criminal law to report another’s wrongdoing becomes more complex when the potential reporter is a professional. Whilst there may be a benefit to the community in more reliable information being obtained, there may be a cost to the individual client who is not able to rely on the professional’s confidentiality. People may filter the information they give to the professional to prevent being reported, or being they do not even go to see the professionals. The recent UK’s Court of Appeal decision in Bowman v Fels  has mitigated the extent of the duty to report. This decision made it clear that there would be no duty to report client’s criminal activity that was discovered during the preparation of litigation.
It is accepted that a citizen has a civic duty to report crime, but to criminalize a failure to do so or following the approach of France shows a degree of mistrust and hostility damaging to social harmony, which literally turns the society into a de facto police state. The idea of imposing duty to report an offence should be well planned as Hong Kong is very sensitive about autonomy and the people are usually against things that are invasive to personal liberty.