SOFIA, Bulgaria-A series of powerful explosions at an army ammunition depot near Sofia Thursday damaged buildings and forced the closure of the country's main airport, officials said.

There was no immediate reports of injuries from the blasts, Emergency Situations Minister Emel Etem said.

The blasts occurred near the village of Chelopechene, just outside Sofia, at 6:30 a.m. (0330 GMT) and were heard throughout the capital.

Smaller explosions continued for at least another two hours. The cause of the blasts was not immediately clear.

Buildings in Chelopechene suffered extensive damage, and authorities closed the nearby Sofia International Airport after debris fell near the runways. It was unclear for how long flights would be suspended.

Defense Minister Nikolai Tsonev said nearly 20 tons of munitions were in storage at the depot.

Emergency teams rushed to the blast site, and people in the area near the depot were urged to evacuate or find a safe place because of the danger of shrapnel.

"Large quantities of conventional ammunition are stored in the facility, but there are no toxic chemicals or radioactive substances stored there," said Nikolai Kolev, a senior presidential aide and former army chief of staff.