The group consisted of officials from the embassies of Britain, Germany, Poland, Russia, Sweden, the Czech Republic, India and Mongolia.

"The weather at the location is not good today. There's a possibility they might not return today at all," said Polish Ambassador Wojciech Kaluza, who sent his deputy.

If everything went as scheduled, they should be back by 6:00 pm (1000 GMT), he told AFP.

The blast reportedly occurred last week in remote Kimhyungjik county in Ryanggang province close to the Chinese border, an area known to have storage for missiles and explosives.

The North said the blast was a controlled explosion to prepare for construction of a hydro-electric power project.

Officials in Washington and Seoul have dismissed speculation that a nuclear explosion took place but other senior officials have said the North's explanation left many questions unanswered.