TAIPEI (AP) - Taiwan officials demanded on Friday (Aug 30) that China disclose information about the disappearance of a Taiwanese man who had reportedly distributed photos of Chinese troops massing equipment just outside protest-racked Hong Kong.

Friends and family have been unable to reach Mr Lee Meng-chu, a volunteer activity organiser with a small township in southern Taiwan, for 10 days, the Taiwan government's Mainland Affairs Council said after receiving pleas for help from Mr Lee's family members.

Communist Party-ruled China often detains people over political matters and may hold them in an unknown location for several months if they are suspected of threatening national security.

"He was able to be contacted while in Hong Kong and then unreachable once he entered mainland China," council spokesman Chiu Chui-cheng told reporters.

"The main thing now is we need to understand his movements and whereabouts, then eventually how to get him safely back to Taiwan."

Mr Lee entered Hong Kong on Aug 18, Taiwan's government-run Central News Agency reported. He apparently transmitted photos to his brother and to the township chief showing paramilitary troops massing equipment on the Hong Kong border with mainland China, the agency said.

The drills conducted in Shenzhen city fuelled speculation that China might send its People's Armed Police to deal with repeated mass pro-democracy demonstrations in Hong Kong.

Taiwan and China have had frosty relations since the Chinese civil war of the 1940s. China sees self-ruled Taiwan as part of its territory, but most Taiwanese have said in government surveys that they prefer autonomy.

Further straining relations, Taiwanese officials have repeatedly spoken out in favour of anti-Beijing protests in Hong Kong.

China is supposed to inform Taiwan when it detains Taiwanese citizens, under an agreement reached in 2009. Taiwanese officials said on Friday that they had received no information on Mr Lee's case.

Mr Lee was part of a volunteer group for Fangliao Township, a fishing community in southern Taiwan, township secretary Lin Ta-min said on Friday. The native of Taiwan's Hsinchu county would gather information on Hong Kong and foreign countries at the town's request as part of its event planning, Mr Lin said.

"Of course, we hope he can come back," he said. "At the start, we told the Mainland Affairs Council to look for him."

The township secretary said he had no information about Mr Lee's schedule in Hong Kong or beyond.

In another recent case, Taiwanese rights activist Lee Ming-che disappeared in March 2017 on a trip to China and surfaced at a court hearing in the southern Chinese city of Changsha in September that year.

The 44-year-old activist, who had discussed democracy with mainland Chinese on social media, was sentenced to five years in prison for his activities.