Explosions ripped through a key military ammunition depot just outside Sri Lanka's capital yesterday leading police to evacuate residents and seal off roads in the area, police said.

There were no immediate reports of casualties at the Salawa military camp where security forces are known to store some of their heavy weaponry and ammunition, including rockets, police said.

Residents in Salawa, 36 kilometres east of Colombo, were seen leaving their homes as police reported shrapnel hitting the main highway. The night sky was lit with an orange glow and the area shook at regular intervals. Flying debris could be seen from three kilometres away.

"We have closed the road and asked all residents to leave out of consideration for their safety," a police officer at the scene told AFP. Firefighters were stopped from reaching the camp as it was unsafe for them to get close to the source of the explosions. The cause of the blasts was not yet known, said the police officer.