The blast at around 10 pm (1400 GMT) caused a small fire and plunged the carriage into darkness as the train was pulling into a station in Taipei.
Among the 25 victims, three sustained serious injuries – with one in a critical condition. Taipei fire officials reported an explosion in a train at around 10 PM on Thursday night.
A local newspaper has reported that witnesses saw a man in his 40s walk inside the carriage, put down a tube-like object and exit the train.
TAIWAN police on Friday said a train explosion that left 25 injured late Thursday was a sporadic criminal case rather than a terror attack.
The explosion unfolded near Songshan Station in Taipei, the country’s capital city.
The self-ruled island’s premier, Lin Chuan, has ordered all the government agencies to form a team to investigate the blast.
Police say they have arrested a suspect, Lin Wen-Chang, 55, of Taipei, whom they have yet to question.
“We are still investigating the suspect’s motive”, the officer said.
“We are now conducting a full investigation”, the national police’s Taipei chief Wang Pao-chang said in a statement.
Passengers rushed off the train once it reached the station, many of them suffering from burns.
Police told local media they found a broken tube with explosive material inside that looked like a firecracker.