Hong Kong police said on Friday they were investigating an internet video clip apparently showing a man forced to walk naked in one of the world's most densely populated neighbourhoods.

Cable TV news reported that the two-minute clip, which it re-broadcast, was posted on YouTube and that it showed a topless man being surrounded by three men who threaten him with a bat.

After taking off his underpants he is ordered to "walk in a circle" and cross a busy intersection before returning to put his trousers back on.

The incident, apparently recorded from an upper-level apartment across the street, takes place on a residential street in Mong Kok, in full view of pedestrians, Cable TV said.

Police said they were concerned and have appealed for the man to come forward and make a statement.

"The case is classified as criminal intimidation and crime officers of Mong Kok district are conducting active investigations," a police statement said.

Mong Kok, on Hong Kong's Kowloon peninsula, is rated by demographers as one of the world's most densely populated areas, with 160 000 people per square kilometre.

AFP