The government late on Thursday warned that anyone getting too close to a a whale that's been spending time off Sai Kung recently risks landing themselves in prison, as it ruled out setting up an exclusion zone to keep vessels away, and said wounds the animal has received don't appear to be fresh.

The Agriculture, Fisheries and Conservation Department said it would step up patrols alongside the police and the Marine Department, and step in to stop boats getting too close when the whale surfaces.

It's warning people who approach it that they could be guilty of wilful disturbance of protected wild animals, with maximum penalties of a year in jail and a HK$100,000 fine.

The department said it "notes opinions to set up some restricted areas to protect the whale. Since the emergence of the whale are sporadic in this large stretch of waters, the area that needs special management will have to be adjusted according to actual circumstances, it is not feasible to implement such a measure without affecting other marine users."

Officials made the comments after discussions with experts from the Ocean Park Conservation Foundation Hong Kong and other conservation groups.

The department said the experts "all agreed that the wounds on the back of the whale were not caused by recent injuries.

"As the whale is in a stable condition, capable of feeding and swimming while the wounds are healing without any behavioural signs of being sick and stranded, there is currently no need for medical help or other intervening action."

It also ruled out the idea of guiding the whale out to open seas, saying that "no feasible, concrete options that are safe and secure" have emerged in its discussions with the conservation groups.

As well as increasing patrols at sea, the department will distribute leaflets and step up patrols at places such as the Sai Kung public pier to encourage people not to join trips to see the whale.

"For the sake of personal safety, members of the public should avoid close encounters with the whale," the statement added. "They should also avoid disturbing the whale appearing in the vicinity when engaging in water sports.

The baleen whale was first spotted in the area around the middle of this month.