Hong Kong police say they are investigating reports that a man was set alight following a heated argument on a day of widespread protests across the city, as videos of the purported attack surfaced online.
Three videos were posted on messaging channels used by protesters showing a man in a green t-shirt arguing with people on a footbridge, reportedly in the northern district of Ma On Shan.
A masked man dressed in black then throws a liquid over the man and sets him ablaze as crowds scatter and the victim frantically tries to remove his t-shirt.

Video posted online show him arguing with a group of young people, before someone douses him with a liquid and strikes a lighter. Source: Twitter
A spokesperson for the Hospital Authority said a man with burns had been admitted to Prince Wales Hospital, the closest hospital to Ma On Shan.
"He's in critical condition," the spokesperson said.
A police spokesperson told AFP that they had received a report on the incident and were investigating.
The videos have not been verified, but the footage was picked up by Chinese state media.

Three videos were posted on messaging channels used by protesters showing a man in a green t-shirt arguing with people on a footbridge. Source: Twitter
The Global Times tabloid uploaded one of the videos to Twitter, a social media platform banned on the mainland, with the caption: "Black-clad rioters in #HongKong set a resident on fire in Ma On Shan on Monday, Hong Kong police confirmed with the Global Times."

Police say they are now investigating the video. Source: Twitter
"Black-clad rioters" is a phrase commonly used by Chinese media to describe pro-democracy protesters.
What sparked the argument is unclear, but the expletive-laden conversation shows the man in green criticising people sympathetic to Hong Kong's democracy movement, and his opponents berating him back.

Police fire tear gas at protesters in Hong Kong during clashes. One man was shot by police during a tense exchange. Source: Kydpl Kyodo
At one point the man in green can be heard saying "none of you are Chinese".
One of his opponents shouts "Go back to the Greater Bay Area", the name for a nearby region of the Chinese mainland across the border from Hong Kong.
- hitting at least one in the torso - during clashes broadcast live on Facebook, as the city's rush hour was interrupted by protests.