A suspected pipe bomb injured at least 25 people on a busy commuter train at Songshan station in Taipei late on Thursday.

Taiwan police bomb squad said that they found a 15 cm-long, broken metal tube with explosive material inside a black backpack. They have, however, primarily ruled out terrorism as the reason for the attack.

Some witnesses said that they heard three blasts inside the sixth carriage of the train that was travelling from Taipei to Keelung in northern Taiwan, before it burst into flames. They also said that they saw a man walk in and leave a bag in the cabin moments before the explosion.

"There was a blast and the carriage went dark. People were panicking and screaming," one passenger told AFP.

The authorities are searching for more than one suspect, Wang Bao-chang of Taiwan's National Police Agency said in a press conference. They are also hunting for a man, wearing black clothes and aged around 40, who was seen by witnesses just minutes before the blast.

The self-ruled island's premier, Lin Chuan, has ordered all the government agencies to form a team to investigate the blast. "It looks like someone did it on purpose," he said.

He also assured the citizens, saying, "We will make our best efforts to investigate this case. Please rest assured that we will provide effective and efficient security for all passengers."