Democratic Senator Jeff Merkley has spoken out against China's human rights record, including Beijing's treatment of Uighurs in the Xinjiang region and pro-democracy protesters in Hong Kong.

A member of the Senate Foreign Relations Committee and co-chair of the Congressional-Executive Commission on China, Merkley's trip to Taiwan was "part of a larger visit to the Indo-Pacific region", the American Institute in Taiwan (AIT) said in a statement.

"The Senator will meet with senior Taiwan leaders and other counterparts to discuss US-Taiwan relations, regional security, trade and investment, and other significant issues of mutual interest," it said.

Merkley will stay in Taiwan until November 27, the AIT said, without providing further details.

The United States is Taiwan's most important backer and biggest supplier of weapons, but like most other countries it does not have official diplomatic relations with the island.

Visits to Taiwan by foreign politicians often elicit an angry response from China, which claims the self-ruled island as part of its own territory and bristles at any attempt to offer Taipei international legitimacy.

Merkley's trip comes as Republican President-elect Donald Trump prepares to take office.

Taipei has publicly congratulated Trump on his victory, joining other governments around the world in trying to get onside with the mercurial magnate, whose diplomatic style is often transactional.