US President Donald Trump has celebrated the 100th day of his second term in office with a campaign-style speech, touting his achievements and targeting political foes.

Hailing what he called a "revolution of common sense", he told a crowd of supporters in Michigan that he was using his presidency to deliver "profound change".

The Republican mocked his Democratic predecessor, Joe Biden, and aimed fresh criticism at the US Federal Reserve's chairman, while dismissing polls that show his own popularity slipping.

Trump has delivered a dramatic fall in the number of migrants crossing illegally into the US, but the economy is a potential political vulnerability as he wages a global trade war.