A series of powerful explosions at an arms dump complex on the outskirts of Sofia rocked the Bulgarian capital on Thursday, panicking thousands and breaking windows, authorities and eyewitnesses said.

The blasts, which happened near the village of Chelopechene, on the eastern edge of Sofia, caused no casualties, Defence Minister Nikolai Tsonev told state national television.

It is not yet clear whether there are any injuries or major damage. The ministry said guards at the military base stocking obsolete munitions for destruction, were evacuated.

Rescuers are unable to reach the main blast site as ammunition continued to explode, police and civil defence officials said.

"This morning at 6.30 am (4:30 a.m. British time) a fire broke out in the area of Chelopechene and explosions followed," the ministry of emergencies said in a statement.

Authorities shut Sofia's international airport to the north-east of the capital until the situation was deemed safe for flights, the transport ministry said. Incoming flights were diverted to the airport in the southern city of Plovdiv.

The site of the military unit was cordoned off. President Georgi Parvanov and other senior officials travelled to the site, while Prime Minister Sergei Stanishev called a cabinet emergency meeting.

The blasts shook apartment blocks and broke windows in eastern districts of Sofia, eyewitnesses said. People ran in panic into the streets.

"The house was shaking, I thought it was an earthquake," a tearful woman, who lives in Chelopechene, told national radio.

Officials urged people to stay at home. "Our checks show that there are no harmful emissions in the air and mass evacuation is not needed," said Valeri Mladenov, head of civil defence in Sofia.