HONG KONG (REUTERS) - Taiwanese staff working at the island's representative office in Hong Kong will begin leaving the Chinese-run city from Sunday (June 20), a senior official said, after the government in the financial hub demanded officials sign a document supporting Beijing's claim to Taiwan.

Chinese-ruled Hong Kong has become another bone of contention between Taipei and Beijing, especially after Taiwan lambasted a security law imposed on Hong Kong and began welcoming Hong Kongers to settle on the island.

Mr Lin Fei-fan, deputy secretary general of Taiwan's ruling Democratic Progressive Party, said only local staff would remain at the office.

"This is because the Chinese Communist Party and the Hong Kong government continue to force our personnel stationed in Hong Kong to sign a 'one China commitment letter' to recognise 'one China'," he said on his Facebook page.

"As a political prerequisite for the visa renewal, we will of course not accept it!"

Mr Lin said Taiwan would never accept "one China" or "one country, two systems", Beijing's way of running Hong Kong under Chinese sovereignty it hopes to one day apply to the island.

A senior Taiwan official familiar with the matter told Reuters seven Taiwan officials will return on Sunday afternoon, with the last remaining official to come back after visa expiry next month.

Taiwan's Mainland Affairs Council said that since July 2018 the Hong Kong government has "repeatedly set unreasonable political conditions for staff visas for our Hong Kong office, demanding the signing of a One China Commitment Letter".

That has prevented staff for the office from staying there or taking up their posts, it added.

"Starting from June 21, the Hong Kong office will adjust its business handling method," the council added, without giving details. It said the office will maintain "necessary operations".

Taiwanese staff will not sign any such "one China" letter, it added.

China sees democratically-ruled Taiwan as part of "one China" and has never renounced the use of force to bring the island under its control.

Last month, Hong Kong suspended operations at its Taiwan representative office, blaming Taipei's "gross" interference in internal affairs, including with its offer to assist "violent" protesters, accusations Taiwan rejected.

Macau's government followed suit on Wednesday, saying it would suspend operations at its representative office in Taiwan.