Police have classified as attempted murder, the case of a man set on fire on Monday afternoon in Ma On Shan.

In a statement issued early on Tuesday morning, police said a 57-year-old man had been seriously injured. It said the incident happened at about 12.55 pm on a footbridge in On Chun Street.

An horrific video circulating online shows the man in a green T-shirt apparently confronting protesters.

The man, who had been voicing pro-Beijing views, and a group of people exchange insults. Then someone steps forward, throws liquid onto him, and sets him on fire. The flames engulf the man's clothes.

Police said, after receiving a report from a passer-by, officers rushed to the scene and found the man with multiple burns. He was admitted to Prince of Wales Hospital in critical condition.

At a press conference on Monday, the Chief Executive Carrie Lam described the act as malicious, inhumane and something that could not be condoned.

The suspect fled and the Commercial Crime Bureau are now investigating.