At least five people have been killed and more than 240 injured in a series of huge explosions at an arms dump near the Albanian capital, Tirana.
They happened as specialists were dismantling obsolete munitions at the site, next to Gerdec village.
The blasts caused injuries and damage in a wide surrounding area, and were heard more than 170km (100 miles) away in the Macedonian capital Skopje.
Some 4,000 people were evacuated and it is feared the death toll could rise.
Rescuers have been unable to reach the main blast site as ammunition continues to detonate at the dump, many hours after the first blast. Special army units have been deployed in armoured vehicles.
The rescue operation was halted after night fell, but is due to resume at daybreak on Sunday.
Hospitals have taken in injured people suffering burns, concussion, broken limbs and cuts from flying glass and shrapnel.
Juela Mecani, a spokeswoman for Albanian Prime Minister Sali Berisha, said a number of homes near the depot had been "completely destroyed", and that the authorities had evacuated all neighbouring villages.
Rescuers had managed to find and save 25 residents who had hidden in a communist-era bunker when the explosions began, she added.
'Ten minutes to flee'
Police said the cause of the explosions was not immediately clear, but terrorism was not suspected.
Mr Berisha's office quoted witnesses as saying the initial explosion was smaller than subsequent blasts, allowing many of the estimated 110 workers on the site to escape.
"Ten minutes passed before the biggest blast and many workers used this time to flee," its statement said.
"The government is trying to identify all the workers, one by one, but the situation is difficult and the explosions continue."
Mr Berisha, a heart specialist, promised an official inquiry into the accident after visiting victims in hospitals in Tirana.
"The problem of ammunition in Albania is one of the gravest, and a continuous threat," Mr Berisha said.
"There is a colossal, crazy amount of it dating back to 1945."
The blasts smashed windows at Tirana's nearby international airport, and prompted a brief suspension of flights.
The base was a central collection point for an arsenal amassed by Albania's former communist dictatorship.
Albania has been offered international medical and other aid
Albania has about 100,000 tons of excess ammunition stored in former army depots across the country, according to Defence Minister Fatmir Mediu.
The military experts at the base where the blasts occurred were being assisted by employees of a US company contracted by Nato to help the Albanian army dispose of surplus munitions.
It is unclear whether Americans or other foreigners were among the victims.
The US embassy in Tirana said it was unable to confirm whether there were foreigners present at the dump.
Countries including the US, Italy, Greece, Macedonia, Turkey and Kosovo have offered medical and other aid to the Albanian authorities in the wake of the explosions.