A blast at an explosives depot in eastern Sri Lanka on Friday killed at least 25 people, including two Chinese road builders and destroyed a police station, the military said.

Three container loads of munitions being stored at a police station in Karadiyanaru, 235 miles (375 kilometres) from Colombo, exploded while some of it was being loaded in a truck by Chinese contractors.

Friday's blast was the first major explosion in Sri Lanka since government forces ended its 37-year-year battle against Tamil Tiger rebels by wiping out the top guerrilla leadership in May last year.

The military said it had ruled out sabotage.

"We completely rule out sabotage. There is no threat to security in that area," military spokesman Ubaya Medawala told reporters in the capital Colombo.

The force of the blast obliterated the buildings and surrounding area, which was littered with rubble, twisted vehicles and bodies.

Witnesses saw a crater about 35 feet (10 metres) deep at the spot where the police station once stood.

Prime Minister D. M. Jayaratne flew to the area to inspect the clean-up operation and visit wounded survivors. President Mahinda Rajapakse, who is on his way to attend the UN general assembly in New York, sent his condolences.

Medawala initially gave the death toll as "over 60" but later revised it down to 25. He said 16 policemen, two Chinese contractors and seven Sri Lankan civilians were killed. Another 54 people were wounded, he said.

"The type of explosives was dynamite that is usually used to blast rocks when building roads," Medawala said.

The Chinese contractors were working for state-run China Overseas Holdings Limited, a construction company carrying out building work in the war-ravaged area, according to police spokesman Prishantha Jayakoddy.

Karadiyanaru is a fishing village that was previously under control of the separatist Tamil Tiger group, which fought for more than three decades for a homeland for the Tamil ethnic group on the Indian Ocean island.

The civil war ended in May last year when government troops crushed the rebels in a military offensive that has since been dogged by war crimes allegations.

Shanthi Udayakumar, a nurse at the nearby Batticaloa hospital, about 15 kilometres from Karadiyanaru, was on duty at the time of the explosion.

"I could feel the tremors of the blast," she said. "Lots of injured people are being brought in."

The blast comes as a high-profile defence delegation led by Sri Lankan Defence Secretary Gotabhaya Rajapakse is touring China.

"Our ties with China remain strong as ever despite what happend (on Friday)," Director General of the Media Centre for National Security, Lakshman Hulugalle told reporters.

Chinese infrastructure companies are highly active in Sri Lanka, fuelling concerns in neighbouring India about the growing influence of China in South Asia.

Chinese diplomats were quickly dispatched to the scene of the blast, China's state Xinhua news agency reported.

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