Security has been stepped up on transport networks including trains, ports and airports across Taiwan after a mystery explosion aboard an underground train in Taipei left around 24 people injured, with 21 of them requiring hospital treatment. The cause of the blast has not yet been identified but authorities have ruled out a technical fault after the blast took place at the Songshan station at around 10pm local time on 7 July.

Some eye-witnesses reported seeing a man in his forties board the sixth carriage of a train, leave a long object and then disembark. A few witnesses said the object was a black luggage bag. The resulting blast started a fire which destroyed much of the carriage. About 10 fire engines were sent to the scene and the fire was soon put out, according to Focus Taiwan News Channel.

Most of those injured suffered burns and were taken in 11 ambulances to nearby hospitals, including Tri-Service General Hospital. The most seriously injured is thought to be a 14-year-old boy who suffered blast wounds to the face. The blast — apparently captured on a nearby CCTV camera and posted on YouTube — also shattered windows causing flesh cuts to at least two passengers. Such was the chaos the exact number of injured is not yet clear.

Taiwan's National Police Agency director-general Chen Kuo-en rushed to the scene in the aftermath of the incident. Kuo-en said explosives measuring 15-20 cm had been found on a seat in the sixth carriage. Police bomb squad chief Lee Tzu-wen said the device was "a 15 centimeter-long, broken metal tube stuffed with explosive material inside a black backpack," according to the Mail. A manhunt is underway for the suspect.

Taiwan's Premier Lin Chuan has established an ad hoc team of relevant government experts to investigate the cause, Channel News Asia is reporting. Security has been stepped up across the country by the transport ministry.