Several US legislators have urged Taiwan to stop tearing down shortwave radio transmission towers which have broadcast uncensored news to China since the 1960s.

The legislators have raised fears the move could reduce the range of the broadcasts by the state-funded Radio Taiwan International(RTI).

On Monday RTI began work to demolish towers at two radio stations in the southern cities of Tainan and Huwei.

The Tainan station, once one of the world's biggest, has 20 signal transmission towers which are each 75 metres (247 feet) high.

"I have been informed that Senators James Inhofe and Bob Corker are concerned about plans that may reduce pro-democracy shortwave broadcasts into mainland China by Radio Taiwan International," US Representative Dana Rohrabacher said in a letter to Taiwan's President Ma Ying-jeou.

Ma initiated the island's ongoing detente with China after being elected in 2008.

"These towers are powerful strategic assets that can broadcast uncensored news and information to all of mainland China," the letter said.

"Any demolitions that would reduce the capability to transmit into China should be halted until alternatives can be fully explored."

The move also raised eyebrows at the Sound of Hope Radio Network, a San Francisco-headquartered radio station which has entrusted RTI to broadcast Chinese-language shortwave programmes to the mainland 17 hours a day.

"Shortwave radio programmes are critical to the people in mainland China, where half of its 1.3 billion population don't know how to use keyboards. Many of them rely on shortwave radio to find the truth," Allen Zeng, president of the network, told AFP.

RTI insisted that despite the demolition of the ageing facilities, its shortwave broadcasts on behalf of clients which also include Radio Free Asia of the United States would continue.

"All the programmes transmitted through the two stations will be moved to other stations which have updated facilities and greater transmission power," an RTI publicity manager told AFP.

She said the demolition, aimed at reducing the number of RTI transmission stations to six, was in accordance with a resolution approved by parliament in 2010 to enhance RTI's efficiency.

Taiwan and China have remained technically at war since their split in 1949 at the end of a civil war, but tensions have eased markedly since Ma came to power. He was reelected in January 2012.