Initial reports by South Korean media said 3,000 people were killed or hurt in the disaster on Thursday at a railway station in Ryongchon, a bustling town 144 kilometres north of the North Korean capital, Pyongyang.

Issuing a rare appeal for foreign help, the secretive Stalinist government in Pyongyang admitted a devastating train explosion killed several hundred people, and it invited aid workers to come see the disaster site near the Chinese border.

The town of Ryongchon was an obscure stop on North Korea's main rail artery to China until the deadly blast seared its name onto the map of a world that knows little about the communist North.

The blast was triggered when two wagons, which were packed with dynamite and being shunted into a siding, hit live electricity wires at the station near the western border with China, a UN official told AFP.

All structures within a 500-metre radius of the explosion were levelled, South Korea's Yonhap news agency said citing witnesses. At the time of the blast, some 500 passengers and railway employees were at the station.

Rescue teams were scouring the rubble of households levelled by the fiery blast that also sent plumes of acrid smoke billowing over the town and rained debris for miles around.

Reuters quoting aid workers says 150 people, including schoolchildren, were killed and more than 1,000 injured.

North Korea declared a state of emergency after the blast that occurred hours after leader Kim Jong-Il passed through the station in his armoured private train on his return from China, Yonhap said.

Given the absence of reliable information emerging from the state, speculation has been building about what caused the accident.

Five international delegates from the Red Cross in Pyongyang would be heading by car to the disaster scene today, probably arriving in the early afternoon, Niels Juel, a Red Cross official in Beijing, told AFP.

Given the poor telecommunications connections in the area, the five delegates might not be able to report on the extent of the damage immediately, he said.

It was likely that the depot's stocks of tents, blankets and water-purification tablets would be released to assist in helping the victims of the explosion, he said.

Residents of Ryongchon, where a train collision wreaked carnage, were living in tents and coping as best they could yesterday as panicky relatives rushed over the border from China to help.

"As soon as the explosion happened a lot of homes collapsed. A lot of people are using canvas or plastic to shield themselves from the weather," said Li Kaisheng, who has spoken with family in the devastated town.

"Many people are living outside in tents. A lot of windows have been shattered and roofs blown off."

Relief teams were headed to the remote corner of North Korea yesterday.

In Washington, US State Department spokesman Richard Boucher said: "We are following the reports of a train accident in North Korea.

"We've seen some reports of very large numbers of casualties from that."

If the reports are confirmed, "that indeed would be very sad and, obviously, we would express our sympathy to whoever was hurt," he said.

Boucher also said that despite tense relations with Pyongyang, Washington would be ready to help.

"We have always been willing to help the people of North Korea with humanitarian needs, (but) we don't know enough about the situation yet to know whether there is any assistance that might be necessary."

Japan's Chief Cabinet Secretary Yasuo Fukuda said: "It is a very tragic accident. We want to express our condolences to the victims."

Japan would decide whether to help after learning details, he said.