Taiwan's defence ministry said it had dispatched fighter jets to monitor two Chinese H-6 bombers that were flying over the Bashi Channel south of Taiwan and the Miyako Strait, near Japan's Okinawa Island.

"We are fully monitoring the situation and taking efficient responsive measures to ensure defence security," it said in a statement.

The scrambling comes a day after Burkina Faso became the second of Taiwan's dwindling number of formal allies to jump ship to Beijing in a month.

China has increased diplomatic and military pressure on the self-ruled island, which it views as a wayward province to be reunified by force if necessary.

Relations have deteriorated between Beijing and Taipei since President Tsai Ing-wen came to power two years ago as her government refuses to acknowledge that Taiwan is part of "one China".

Tsai's tenure has already seen the loss of three allies to China, with the Dominican Republic, Panama, and Sao Tome and Principe all switching allegiance since 2016.

Although it was not immediately clear if Burkina Faso and China would establish diplomatic relations, Beijing has welcomed the move by the west African state.

Taiwan's Mainland Affairs Council, which is in charge of China ties, announced late Thursday that Chinese officials applying to visit the island would be subject to tighter screening, without elaborating.

The move aims to "prevent the Chinese communists from dividing and disturbing social order in Taiwan with their unification propaganda measures," it said in a statement.

Taiwan now has just 18 formal allies who recognise its government instead of Beijing.

For its part, Beijing has been incensed by a recent warming in relations between Taiwan and the United States, which remains its most powerful ally and arms supplier even though it has no official diplomatic ties.

President Tsai warned China Thursday that Taiwan would not tolerate what she called its "crude behaviour to undermine our sovereignty".

Taiwan's Foreign Minister Joseph Wu tendered his resignation after Burkina Faso's announcement, but said Friday that he would stay on in the position at the president's request.