Former U.S. Rep. Tom Tancredo is entering Colorado's Republican gubernatorial race, bringing a familiar hard line on immigration and drawing an early barb from Democratic front-runner U.S. Rep. Jared Polis.

Tancredo will launch his third bid for governor on Wednesday, according to documents obtained by 9NEWS.

Tancredo is a contributor to conservative Breitbart News, run by Steve Bannon, the former adviser to President Donald Trump. He said he'd welcome Bannon's support if he needs it.

Tancredo rejoined the Republican Party this year after leaving in 2010 to run for governor as the American Constitution Party candidate. He left again in 2015.

Polis issued a statement saying Tancredo "has spent his career championing hate groups, vilifying immigrants, and seeking divisiveness."

Nine Republicans and seven Democrats want to succeed term-limited Democratic Gov. John Hickenlooper.