A Taiwan tourist was among three people in critical condition on Saturday after a rush hour arson attack on a Hong Kong subway train the previous night, officials said, with one man with a history of mental illness arrested for the crime.
A total of 18 people were injured in the incident which occurred at 7:15 pm on Friday, while police said they had seized suspected liquid accelerants from the scene.
Police have ruled out the possibility of a terrorist attack and said the man acted alone, with investigators looking into his mental state.
"We visited a female tourist from Taiwan, her condition is still considered critical and is in intensive care," the city's number two official Matthew Cheung told reporters.
"To our knowledge, she has a friend in Hong Kong, and that friend has notified her family, and that they are on their way to the city," Cheung, the chief secretary, said.
Health secretary Ko Wing-man said the three in critical condition were on breathing apparatuses.
Ko added that the suspect had a history of mental illness.
"In the long term, his condition was stable, but recently he was supposed to receive treatment but he missed it," Ko told reporters.
Video footage showed chaos on the platform of the packed Tsim Sha Tsui station, with a train carriage on fire and one man lying on the floor with his clothes ablaze as bystanders tried to help him.
Images broadcast on Cable Television news also showed multiple people with burn injuries, as emergency personnel carried out rescue operations.
Cable also reported that a 15-year-old high school girl received burn injuries to her legs.
"I heard loud cries, and the smell of the fumes didn't smell like a normal fire -- it had a chemical smell," an eyewitness identified as Mr Chow told reporters at the scene.
"Once I inhaled it, it burned the throat," Chow said.
Police said they had arrested a 60-year-old man surnamed Cheung for arson.
"The mental condition of the arrested person is one of (the) directions of (the) police's investigation," a government statement said Saturday.
Reports said the suspect was not on good terms with his family and had previously been arrested for minor crimes such as gambling.
The South China Morning Post had earlier reported that the man tried to light a Molotov cocktail and said "burn you to death" before he took out the bottle.
Cable Television reported the man had said loudly some people had harmed his son and he needed to take revenge, and that he had doused his trousers with thinner liquid.
Local media said the suspect was among those in critical condition, but police would not confirm the reports.