Two Germans were among four people killed when fireworks being prepared for Hanoi's millennium celebrations exploded, a source with the Vietnamese fireworks importer told AFP today.

Other official Vietnamese sources separately said two Germans died in the Wednesday morning blast outside My Dinh Stadium where the Sunday night celebration is set to take place.

Berlin's embassy in Hanoi declined to comment Thursday and referred inquiries to the Foreign Office in Germany.

"Two Germans are among the four victims of Wednesday's explosion of two fireworks containers in My Dinh," said the employee at the Hanoi offices of Interserco, the International Commercial Investment and Services Company.

The government said Interserco had imported the fireworks for the celebration.

Singapore's foreign ministry said one of the dead may have come from the city-state, while official Vietnamese sources identified the other fatality as a native of Vietnam.

Local media showed pictures of a thick cloud of smoke after the blast which sent large chunks of metal flying and shattered windows at least 200 metres (yards) away.

Reasons for the blast "remain unknown," said the Interserco employee, asking to remain unidentified.

"We are waiting for a final conclusion by the investigators."

The government has blamed the blast and fire on "carelessness during the process of transport".

Despite Wednesday's tragedy, local media reported that a rehearsal took place Wednesday night at the stadium ahead of Sunday's grand finale.

The show featuring lasers and thousands of performers depicts Vietnamese history and will cap 10 days of exhibitions, cultural performances and other events for Hanoi's 1,000th birthday.

"The event will finish with a magnificent display of fireworks in several places around Hanoi," the website of Voice of Vietnam radio reported.