Protesters occupy the departure hall of the Hong Kong International Airport during a demonstration on August 12 in Hong Kong.

Chinese state media called on Beijing on Wednesday to deal with protests in Hong Kong more decisively after a reporter from one of China's largest government-backed newspapers was caught up in overnight clashes.

Ten weeks of increasingly violent clashes between police and pro-democracy protesters, angered by a perceived erosion of freedoms, are posing one of the biggest challenges for Chinese President Xi Jinping since he came to power in 2012.

Demonstrators and riot police clashed at Hong Kong's airport late on Tuesday after flights were cancelled for a second day. Protesters at one point held a man who Chinese media have said was a reporter from China's Global Timesn ewspaper.

A front-page commentary on the overseas edition of the Communist Party's official People's Daily newspaper said on Wednesday Hong Kong had reached a critical juncture.

"Using the sword of the law to stop violence and restore order is overwhelmingly the most important and urgent task for Hong Kong!" it said.

Another commentary by a Shenzhen University researcher, published by the China Daily, said the central government should deal with Hong Kong issues more decisively.

Demonstrators say they are fighting the erosion of the "one country, two systems" arrangement that enshrined some autonomy for Hong Kong after China took it back from Britain in 1997.

U.S. President Donald Trump said on Twitter overnight the Chinese government was moving troops to the border with Hong Kong and urged calm.

However, Chinese state media has stopped short of calling for military action to deal with the protests.

"Extreme political ideas have found frequent expression in Hong Kong, with some even raising 'Hong Kong independence' slogans recently. Which means the 'one country, two systems' principle faces a new challenge," Chinese author Li Peiwen said.