A brief state news agency report on Saturday gave no details of casualties, but said the damage was "very serious".
Britain's Foreign Office had earlier quoted unnamed North Korean officials saying the death toll was several hundred in Thursday's blast, which razed part of the town of Ryongchon, near the Chinese border.
"An explosion occurred at Ryongchon railway station in North Phyongan province on 22 April due to the electrical contact caused by carelessness during the shunting of wagons loaded with ammonium nitrate fertiliser and tank wagons," the Korean Central News Agency (KCNA) said.
It said: "Pyongyang appreciates the willingness expressed by the governments of various countries and international bodies to render humanitarian assistance."
Soon after, South Korea announced an emergency aid of $1 million and said its officials would meet North Korean counterparts on Monday for discussions.
China also offered $1.2 million in emergency relief supplies to North Korea, including food, medicine and tents.
In Geneva, the United Nations Office for the Coordination of Humanitarian Affairs (OCHA) said it had received a request for international help from Pyongyang on Friday afternoon.
"We need the help of the international community: emergency relief," envoy Pak Gil Yon said.
"We need the help of the international community: emergency relief"
Pak Gil Yon,
North Korea's envoy to the UN
Pyongyang rarely reports on accidents and only belatedly sought outside aid after floods and a famine in the 1990s.
The United States, which labelled North Korea part of an "axis of evil" with Iran and pre-war Iraq, said it was willing to help despite a standoff over Pyongyang's suspected nuclear arms programme.
Reliable figures on the number of dead have so far been scant. The OCHA in Geneva, quoting figures from the Red Cross, said 50 bodies had so far been recovered from Thursday's blast.
But earlier the regional director of Concern, a relief agency with an office in Pyongyang, said 150 people had died, including some schoolchildren.
Russia's Itar-Tass news agency quoted the Russian embassy in Pyongyang as saying four of its diplomats would go to the blast site on Saturday to get a clearer picture of what happened.
International aid agencies have also been invited to visit the scene of the train blast on Saturday.
South Korean media, quoting witnesses and Chinese sources, put the toll at up to 3000 people killed or injured.