There are calls for greater safeguards in Taiwan after at least one device used by the military for its missiles was sent for repair in China.

An optical instrument used for launch measurements for Taiwan's Hsiung-Feng III anti-ship missiles was shipped to its manufacturer in Europe.

It was then sent back to Taiwan from Shandong province in eastern China, Taiwanese media reported.

Last year Beijing intensified military activity around the island.

China sees Taiwan as part of its territory and has vowed to unify to it by force if necessary. Self-ruled Taiwan sees itself as distinct from the mainland.

President Tsai Ing-wen has announced new plans to bolster Taiwan's defence in the event of an attack from Beijing, including extending mandatory military service from four months to one year.

In a statement, Taiwanese missile developer the National Chung-Shan Institute of Science and Technology said the device had been shipped to Switzerland by the company that had originally supplied it to the Taiwanese military.

From there it was diverted for repair at the manufacturer's Asia maintenance centre in the Chinese city of Qingdao, it said.

The institute said it had removed memory cards before sending it to Europe and had also run information security checks on the device after its return and had no concerns over possible information leaks.

Dr Su Tzu-yun from Taiwan's Institute of Defence Security Research said the optical devices were not direct missile components but said Taiwan had to be more careful anyway.

"Taiwan must be more strict and careful in its contract management," he said. "Of course we would not want such equipment to be sent to China for repair."

The tool, a theodolite, is used to measure precise geographical location for missile launches as well as the angle and direction of the launchers, Dr Su said.

"It's like when you buy a computer, it's a device you put on the desk to go with the machine," he said.

He suggested that the manufacturer had not been aware the devices, purchased by a supplier in Taiwan, had subsequently been used for military purposes.

It is not the first time concerns over the security of Taiwan's missile programme have been raised. Last year, three people at two Taiwanese suppliers were sentenced to between four and 10 years in prison for using products from China to fake missile components supposedly to be made by US manufacturers.