Thousands of people have been evacuated after explosions ripped through a munitions dump in south-east Ukraine.
Three people died, unnamed officials and hospital staff were quoted as saying, but the Defence Ministry has not confirmed the death toll.
Reports speak of flames leaping up to 300m (984 feet) high at the depot – which is only 40km from one of Europe’s biggest nuclear power stations.
Ammunition was continuing to explode on Thursday night, reports said.
Some of the debris and ordnance has been thrown 10km (six miles) away, says the BBC’s Helen Fawkes in Kiev.
Ordnance began exploding during a fire at the military base near the city of Melitopol in Zaporozhye region at about 1300 (1000 GMT) on Thursday.
The first building affected was said to store anti-tank mines. Other reports speak of artillery shells and rockets exploding.
Soon after the blaze started, there were several huge explosions which destroyed many buildings within a 3km radius of the military base, including a local railway station. Some two dozen fire trucks rushed to the scene, along with about 120 firefighters and 100 soldiers, but continuing explosions severely hampered the operation.
According to witnesses, explosions could be heard every few seconds hours after the fire began.
Nearly 10,000 people from villages within a 10km exclusion zone around the depot have been evacuated.
The emergency ministry said the explosions sent burning debris up to 10km away, causing more fires to start.
Rail traffic has been blocked on the main line linking Crimea to the Russian capital, Moscow, and local roads are closed.
A state of emergency has been declared in Melitopol – about 600km (370 miles) south-east of the capital Kiev – and authorities are telling people to stay indoors.
President Leonid Kuchma has ordered a criminal investigation into the incident.
Earlier this year, the Prosecutor General’s Office warned military leaders about the potential dangers at the base.
The chief of the general staff of the armed forces has appeared on national television to apologise publicly to Ukrainians.