China says four officers were killed when a marine surveillance plane crashed into a mountain along the country's east coast.

State Oceanic Administration said the accident occurred Tuesday during a routine mission to monitor conditions in Zhejiang province whose coastline is dotted with hundreds of islands.

It said the wreckage was found early Tuesday evening after a search involving 18 ships and four helicopters. The type of plane was not identified, although the China Marine Surveillance agency operates aircraft including helicopters and the Chinese-made Harbin Y-12 turboprop.

The agency is one of four under the State Oceanic Administration used to patrol and carry out law enforcement missions along China's vast coastline, as well as in waters claimed China in the South China and East China Seas.