The National Basketball Association has severed ties to a training centre in China's western Xinjiang region, where Beijing faces growing international condemnation over its treatment of minorities.

In a letter published online by Senator Marsha Blackburn, the US league also said it had lost "hundreds of millions of dollars" in revenue after Chinese broadcasters dropped its games last year amid a bitter row triggered when a Houston Rockets executive expressed support for Hong Kong pro-democracy protests.

The NBA statements were contained in the letter dated July 21 to Blackburn that was posted on the Tennessee politician's official Senate webpage on Wednesday.

Signed by NBA Deputy Commissioner Mark Tatum, it was sent in response to questions raised by Blackburn about NBA involvement in Xinjiang, described by the senator as "one of the world's worst humanitarian zones".

China is in the midst of a bitter falling out with the United States on a range of fronts, including human rights, trade and Hong Kong.

"The NBA has had no involvement with the Xinjiang basketball academy for more than a year, and the relationship has been terminated," Tatum wrote in the letter, which was confirmed as genuine by an NBA official.

More than one million ethnic Uighurs and other minorities, mostly Muslim Turkic peoples, have been herded into Xinjiang internment camps where they undergo political indoctrination, according to human rights groups and experts.

The NBA's lucrative broadcast and merchandise interests in China went into a tailspin in 2019
The NBA's lucrative broadcast and merchandise interests in China went into a tailspin in 2019 AFP / HECTOR RETAMAL

The existence of the camps had been revealed in recent years and appear aimed at taming long-time opposition by many Uighurs -- marked a spate of violent incidents -- over political and religious repression by Beijing.

The NBA's lucrative broadcast and merchandise interests in China -- the league's most valuable market outside of the United States -- went into a tailspin after Rockets general manager Daryl Morey's tweet regarding Hong Kong protesters last October.

The comments infuriated the Chinese government and basketball fans and caused state broadcaster CCTV to stop showing matches.

"The financial impact of NBA games not airing on television in China has been significant," Tatum wrote.

"We estimate the loss of revenue to be in the hundreds of millions of dollars."

China is under mounting pressure from the United States and other trading partners over issues including Xinjiang and a new security law that Beijing imposed in Hong Kong, sparking fears that civil liberties in the semi-autonomous Chinese territory will be crushed.

The NBA has been in shutdown since March, when the coronavirus pandemic erupted across North America.

The league is relaunching its season with teams based in Orlando for the remainder of the regular season and the playoffs.