When Tsai Ing-wen becomes Taiwan's president later this month, she will end a period of unprecedented rapprochement with rival Beijing -- and China is already ramping up the pressure on her new government.

Tsai's Democratic Progressive Party (DPP) is traditionally pro-independence and refuses to chime in with Beijing's message that self-ruling Taiwan is part of "one China".

Tsai won the presidency by a landslide in January as voters wary of closer China ties turned their backs on the ruling Beijing-friendly Kuomintang.

Since then, with a transitional government in power until Tsai is officially inaugurated on May 20, Beijing has increasingly made life difficult for Taiwan in what observers say is an early challenge to Tsai's presidency.

Taipei was furious in April after Taiwanese fraud suspects were deported to China from Kenya and Malaysia, rather than back to their home territory.

China also recognised Taiwan's former ally Gambia in March, ending an unofficial diplomatic truce between the two sides.

Taiwan has haemorrhaged allies in recent decades as they jump ship to align with a rising China, and is now only recognised by 22 states.

"Beijing wants to teach Tsai a lesson. The incidents are intentional and send a very clear message that it is tightening the screws," said Francis Hu, a political scientist at Taiwan's Tunghai University.

Some local tourism operators have reported a decline in Chinese visitors since January -- after a boom prompted by the thaw in ties -- with some speculating they are being discouraged from heading to Taiwan.

Tsai's KMT predecessor, outgoing President Ma Ying-jeou, agreed there was "one China", but with different interpretations on each side of the strait.

That earned him a landmark meeting with Chinese President Xi Jinping and a slew of trade deals.

Beijing wants Tsai to do the same.

"It's their bottom line," said Hu.

However, faced with increasing voter scepticism over China relations and a staunch pro-independence wing in her own party, it is a demand she is unlikely ever to meet.

- 'A cold peace' -

Taiwan split from mainland China in 1949 after a civil war, but has never formally declared independence, despite being a fully-fledged democracy.

Beijing still considers the island part of its territory awaiting reunification, by force if necessary.

China has been clear about its distaste for Tsai since she won the presidency -- on the day she was voted in, Beijing warned her against making any move towards formal independence.

For her part, Tsai has vowed to maintain the "status quo" with China and has given a measured response to the recent bouts of diplomatic sparring.

But she has also made clear future cross-strait policy will be "based on the principle of democracy and people's desires".

Tsai now has "a huge balancing act" to perform, said Kerry Brown, director of Lau China Institute at King's College London.

Not only must she handle Beijing and appease the electorate, she must also reassure Washington -- Taiwan's greatest ally and leading arms supplier -- that she will not rock the boat in the region, said Brown.

Her inaugural speech on May 20 is likely to reflect that high-wire act.

"She will try to maintain the moral high ground, to continue to have support from the US and the international community, by sounding reasonable, moderate, and diplomatic," Brown said.

"But she will also send Beijing a message that she will not be bullied and humiliated in front of her own people."

Observers predict Beijing will keep up the pressure when Tsai takes office, with the possible suspension of high-level dialogue between the two sides and a push for Taiwan's further diplomatic isolation.

Few believe there will be any drastic action in the near future.

"I think the most likely scenario is that China will not be satisfied but still find it acceptable," said Tang Shao-cheng, a political scientist at National Chengchi University in Taipei, who believes Tsai will toe a line in her rhetoric to calm US nerves.

However, Beijing's inherent lack of trust could lead to deterioration further down the line.

"It will be 'cold peace' in the short term -- and hot challenges in the long term," said Tang.