QINHUANGDAO, Hebei -- Chinese emergency services carried out their largest ever exercise on Tuesday to tackle an oil spill in the Bohai Sea to test their ability to protect the ocean environment.

The drill, which began at 9.30 a.m., involved a scenario in which a 10,000-ton oil tanker exploded and spilt 500 tons of oil.

Soon after the oil tanker Tianpeng "exploded", a fireboat arrived to fight the fire and a helicopter hovered above to spread chemicals to control oil spill, followed by more vessels and another helicopter.

The "spill" comprised fire-fighting foam that would cause no pollution to the sea.

The exercise ended at 11:00 a.m. after the "spill" was cleared. Vice Minister of Communications Xu Zuyuan said it was "successful".

"The exercise tempered our oil spill response team, improved the government's ability in handling such accidents and helped marine environment protection," Xu said.

A total of 500 people participated in the exercise and 20 vessels and two aircraft were involved in the drill off the coast of north China's port city of Qinhuangdao, Hebei Province, in clear and calm conditions.

A college student, one of 300 volunteers cleaning the beach, said, "I am amazed by the quick response. It would be great that all oil spills are handled so promptly."

Near the beach is a stadium in which football matches will be held during the 2008 Olympic Games.

Liu Gongchen, executive deputy director of the Maritime Safety Administration of the Ministry of Communications, said organizers chose June 5 for the drill as it is the World Environment Day, in a bid to improve the awareness of marine environment protection.

Oil exploitation and marine transportation have developed rapidly in China, bringing increased risk of oil spills.

The exercise was held near the recently discovered partly-offshore Nanpu block, which is estimated to have one billion tons of reserves, held by the Jidong Oilfield of the China National Petroleum Corporation (CNPC) in Caofeidian of Tangshan City, Hebei Province.

The discovery is expected to reduce the country's reliance on oil imports, but many are concerned about possible pollution of the Bohai Sea.

China experienced 2,635 oil spill accidents in its seas and along its coastal areas from 1973 to 2006, including 69 major accidents each involving at least 50 tons of oil and with a total of 37,077 tons. On average, two such accidents took place per year, with each spill involving 537 tons of oil.

The Bohai Bay, Yangtze River Estuary, Taiwan Strait and Pearl River Estuary are four major Chinese sea areas at the greatest risk of oil spills.

Chang Xuejun, vice general manager of Jidong Oilfield Company, said, "Such exercises are necessary to ensure we do our best to prevent environmental disasters."

The Bohai Sea covers 78,000 square kilometers of sea that is almost enclosed by the Shandong and Liaodong peninsulas.

It boasts rich fishery, sea salt and oil resources, and has 26 cities and about 100 ports along its 3,000-km coastline. However, experts have warned Bohai is "dying" due to heavy pollution.