Videos showed chaos on the platform at Tsim Sha Tsui station, with a cabin on fire and one man lying on the platform with his clothes ablaze as bystanders tried to help him.
"According to our preliminary investigations and the statements of the injured, we suspect there was a resident (who) had lit combustible agents," deputy chief fire officer Yau Chi-on told reporters.
A government spokeswoman told AFP that of the 17 injured, two were in a critical condition. Yau said the victims had suffered serious burns and inhaled harmful fumes.
"We have arrested this person for committing arson," police district commander Kwok Pak-chung told reporters, adding that the man was a 60-year-old surnamed Cheung.
"According to investigation up until now, we believe this incident was related to the personal issues of one person, an independent incident. No information at this point shows that it was an act of terror or an attack targeting public transportation," he said.
"When one of my colleagues brought one of the injured persons to the hospital, the person declared he was involved with the fire and that he had lit the fire," Kwok said.