Vietnam's environmental police have seized a record haul of over 1,000 endangered sea turtles which were being prepared for illegal export to China, an official said Tuesday.

"The turtles were all dead," Le Hong Thai, an official of the Ministry of Public Security's environmental police department, told AFP.

"They were meant to be processed into handicrafts for export to China," he added.

The raids were made on Wednesday last week in the resort town of Nha Trang on Vietnam's south-central coast.

"The case is under investigation, so we cannot reveal the number of detainees or any other details," Thai said.

Marine turtles are fully protected under Vietnamese law.

Hunting and trading, including the storing, of any of the five native species is a criminal offence, according to local media reports.

Scores of Vietnamese have been arrested in regional waters over the past years for catching or trading sea turtles.

Nguyen Phuong Dung, the director of conservation group Education for Nature-Vietnam, welcomed the raid but said it must be followed with legal penalties for those involved.

Courts "need to send the message that Vietnam is serious about prosecuting and punishing" crimes involving endangered species, she said in a statement.

Environmental groups say Vietnam is one of the world's worst countries for trade in endangered species -- an accusation which it denies.

Police regularly seize hauls of ivory, rhino horn and exotic species including pangolins and tigers, but conservation groups say these represent just a small part of the trade passing through the communist country.