Superstar LeBron James was to lead his Los Angeles Lakers against the Brooklyn Nets in Shanghai on Thursday night, the first of two pre-season matches held each year to build on the league's already huge popularity in China.

But the intense Chinese backlash against the world's top basketball league over its attitudes on free speech and Hong Kong's democracy movement has thrown the games -- and the NBA's larger interests in China -- into doubt.

In an open letter, a bipartisan set of US lawmakers urged the NBA on Wednesday to suspend all activities in China until Chinese firms and broadcasters end their various boycotts of the league.

The open letter urged NBA Commissioner Adam Silver, who came to Shanghai for Thursday's game, to "take a stand."

"It's not unreasonable to expect American companies to put our fundamental democratic rights ahead of profit," said the letter.

The NBA did not immediately respond to an AFP request for a status update on Thursday's game.

The controversy was sparked by a since-deleted tweet from Rockets general manager Daryl Morey supporting Hong Kong pro-democracy protesters.

Silver and the NBA initially responded to Morey's Friday tweet with statements that American politicians branded as kow-towing to China's Communist regime to protect league profits.

Rockets guard James Harden, in Japan for another exhibition game, also apologised to China, even though he did not send the tweet.

Anger over free speech vow

But, under mounting pressure in the United States, Silver made a strong defence of free speech and American values that provoked outrage in China.

"The long-held values of the NBA are to support freedom of expression, and certainly freedom of expression by members of the NBA community," Silver said in Japan.

"I understand there are consequences from that exercise of, in essence, his freedom of speech. We will have to live with those consequences."

Morey and Silver have been lashed in the Chinese state-run press for their comments, while portraying the issue as a clash of values between China and the US.

The NBA's China sponsors have severed ties and Chinese netizens have called for boycotts.

Actions by local authorities and the NBA in the lead-up to the Chinese exhibition games, the second of which is slated for the southern city of Shenzhen on Saturday, have further fuelled concerns they will be cancelled.

On Wednesday, crews rappelled down glass-and-steel office buildings in Shanghai's financial district to peel off 13-storey promotional images of James and other players.

Meanwhile, workers at the game venue pulled down NBA, Nets, Lakers, and corporate logos.

The NBA also has cancelled each one of a series of press or public activities in Shanghai in the lead-up to the game, with no explanation.

An event on Wednesday bringing the media together with players -- who would surely have faced sensitive questions over the controversy -- was called off just 10 minutes before start time.

Hong Kong has endured nearly four months of protests that were ignited by a now-scrapped plan to allow extraditions of criminal suspects to be tried by China's opaque courts.

They snowballed into a movement calling for more democratic freedoms, the biggest challenge to China's rule of Hong Kong since its handover from the British in 1997.

Chinese state media has repeatedly warned foreign firms against voicing support for the protesters, warning it could cost them access to China's market of 1.4 billion people.

The People's Daily, mouthpiece of the ruling Communist Party, on Wednesday slammed a transport app available on Apple's store that it alleged helped protesters identify police in Hong Kong.

US jewellery brand Tiffany and Hong Kong's flagship airline, Cathay Pacific, have also been heavily criticised in China.