Police arrested a man over a suspected arson attack on Friday after fire broke out inside a train at one of Hong Kong's busiest subway stations during rush hour, injuring at least 17 people, including two who are in a critical condition.

A 60-year-old man surnamed Cheung, who was seriously injured in the incident, admitted he started the fire while the train was headed to the busy Tsim Sha Tsui shopping district, district Police Commander Kwok Pak-chung told reporters.

"While he was on the way to the hospital he mentioned some personal reasons, but he was incoherent. What he said did not make much sense," Kwok said.

He said there was so far no information to suggest the incident could be described as an act of terrorism. The Counter Terrorism Response Unit which was patrolling nearby at the time of the incident was at the scene quickly to assist, he said.

Online media footage, which Reuters could not independently verify, showed people beating out the flames on a man's legs as he lay on the platform. Kwok told reporters the man, whose trousers appeared to be completely burned, was likely to be Cheung.

Another video showed flames burning several items scattered inside the train. It then showed a crowd on the platform who appeared calm as they pointed their phones at the fire. A fire alarm sounded in the station and a man could be heard shouting: "Let's go, let's go, let's go."

Two passengers in the underground train as it crossed the Victoria Harbour told Reuters they saw a lot of smoke.

"Suddenly a lot of thick white smoke swarmed over us. People started covering their noses and mouths. But people were calm. Nobody screamed," said passenger Nigel Ngai, 30. He added that the smoke smelled like burned plastic.

"I didn't know if it was a terrorist attack," he said.

Another passenger, 28-year-old Ms. Chau, said the experience was "a little scary" but people exited the train calmly. "There were many people and it was impossible to run," she said.

Hong Kong leader, Chief Executive Leung Chun-ying, said in a statement he was "highly concerned" about the incident and has asked the relevant departments to investigate.