HONG KONG - Half of Hong Kong's subway trains are not fitted with closed-circuit TV cameras, the train operator has admitted in the wake of Friday's rush-hour arson attack onboard a train, prompting the government to announce a probe on ways to improve security.

A man tried to set fire in a train carriage at the crowded Tsim Sha Tsui station, injuring 19 people including himself as well. Three of those injured, including a Taiwan tourist, remained in critical condition on Saturday (Feb 11).

The man, who is named as 60-year-old Cheung Kam Fai and said to be mentally ill, was arrested.

Police on Sunday (Feb 12) laid a holding charge against him with one count of arson, the government said in a press release. The case will be mentioned at Kowloon City Magistrates' Courts in his absence on Monday.

Mass Transit Railway (MTR) operations director Adi Lau said on Saturday CCTV cameras were not installed on the train involved, nor on trains that came into service before 2004, reported South China Morning Post.

"New batches of CCTV-equipped trains would arrive and be ready for service in 2018 at the earliest," Lau was quoted as saying.

Transport minister Professor Anthony Cheung said the MTR Corporation, which operates the city's subway system, had formed an investigation panel to study how the blaze was handled and possible improvement measures, SCMP reported.

An initial report would be submitted to the government in about a month.

Lawmaker Michael Tien, who heads a parliamentary transport panel, urged the MTR, which logs some 5 million commuter journeys each day, to install CCTV cameras on all trains and review its surveillance systems immediately.

"If there was CCTV on the train, the MTR staff would have known what happened immediately and have the fire extinguishers ready by the door before the train arrived at the platform," Tien was quoted as saying by SCMP.

The attack suspect, Cheung Kam Fai, allegedly murmured "burn you to death" on the packed train before he lit a bottle of flammable liquid. He was still in a critical condition on Saturday night.

Health authorities said Cheung - who is aged 60 and diagnosed with delusional disorder in 2007 - was due to undergo a check-up but missed his appointment on the day of the attack.

It is understood that he lived with his wife and son in Chai Wan. Police contacted the family on Friday as part of their investigation.