Some 120 people have been killed and many others injured in a fire on an underground train in the South Korean city of Daegu.

Authorities say firefighters have reached two burnt-out carriages of the train containing the remains of about 70 people, which is in addition to the 50 or so bodies already recovered.

The bodies were all in a state of being difficult to identify Cho Hae-nyong, Daegu mayor

In addition to those confirmed dead, between 70 and 100 people are reported to be missing and more than 100 people have been injured, officials said.

Thick black smoke and the toxic fumes of burning plastic confronted thousands of rescuers who rushed to the scene.

According to eyewitness reports, a man started the fire by setting alight a milk container containing flammable liquid in a carriage.

"When the man tried to use a cigarette lighter to light the box, some passengers tried to stop him. Apparently a scuffle erupted and the box exploded into flames," Kim Byong-hak, a police lieutenant in Daegu, told the Associated Press (AP) news agency.

Police said they were treating the incident as arson and that a 56-year-old man had been arrested.

Identification problem

As the fire spread through the six-carriage train, a second train that had halted in the station also caught fire.

Rescue efforts were hampered by smoke

YTN television network said some of the bodies had been burnt beyond recognition.

"There were bones scattered on the floor mixed with people's burned belongings," firefighter Park Chang-shik was quoted as saying.

Daegu Mayor Cho Hae-Nyong said the corpses were "all in a state of being difficult to identify".

Pictures showed the charred frames of subway carriages and a platform littered with shoes and discarded belongings.

The injured have been rushed to hospitals, where some are reported to be in a serious condition.

The authorities say the fire was extinguished by 1300 local time (0400 GMT) - about three hours after it started.

Motive sought

One police officer said the suspect was believed to have mental health problems.

"It is not known immediately what has motivated him. We believe he is mentally ill. He is known to have been treated at a mental hospital," Daegu police station chief Suh Hyon-soo told AP.

South Korean President Kim Dae-Jung sent a message of condolence to the victims, the president's office said.

Daegu - about 200 kilometres (125 miles) south-east of the capital, Seoul - is South Korea's third-largest city and was one of the host cities for last year's football World Cup.

Authorities in Seoul have stepped up security at subway stations, fearing a possible copycat attack.

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