Taiwan's opposition leader Cheng Li-wun is on a rare visit to China at the invitation of President Xi Jinping which as she says is for promoting cross-strait "peace."

"The purpose of this visit to mainland China is precisely to show the world that it is not just Taiwan that unilaterally hopes for peace," said Cheng, who is the chairperson of the largest opposition party, Kuomintang (KMT).

"I believe that through this journey for peace, everyone is even more eager to see the sincerity and determination of the CPC Central Committee to use peaceful dialogue and exchange to resolve all possible differences between the two sides," she added, referring to the initials of the Communist Party of China.

"To preserve peace is to preserve Taiwan," Cheng told a news conference at KMT headquarters in Taipei, when asked about her priorities for the trip.

"Goodwill must be built up and mutual trust needs to be expanded, step by step, by both sides."

Cheng is visiting China for six days. She is expected to go to Shanghai, Nanjing and Beijing where she hopes to meet Xi. Beijing has not commented on a possible meeting.

What makes Cheng's visit to China controversial?

This is the first time a Taiwanese opposition leader is visiting China in a decade.

KMT encourages closer relations with China, which claims Taiwan as its territory and has threatened to use force to seize it.

Critics have accused Cheng of being too supportive of China. In October, her rise to the top of the KMT drew a congratulatory message from Xi.

Her trip to China comes ahead of a meeting in Beijing between Xi and US President Donald Trump scheduled to take place in May.

Cheng's visit also comes at a time when the opposition-controlled parliament has stalled attempts by Taiwan's government to pass the $40 billion special defense budget.

The US has been building pressue on Taiwanese opposition lawmakers to support a proposal for defense purchases, including US weapons, to deter a potential Chinese attack.

Edited by: Elizabeth Schumacher