PM rejects China rhetoric on HK protests

Prime Minister Scott Morrison has rejected China's claim that mass protests in Hong Kong are showing "sprouts of terrorism" and called for a peaceful resolution to the 10-week stand-off.

Thousands of travellers remain stuck in the Chinese territory after anti-government protesters forced the closure of its busy international airport on Monday.

Protesters made their way back to the airport on Tuesday afternoon.

Australia's Department of Foreign Affairs and Trade advised on Tuesday of "significant disruption, including the cancellation of flights" and urged all travellers to check their flight status.

DFAT's level of travel advice remained at "exercise a high degree of caution".

On Tuesday evening, all remaining flights at Hong Kong airport were cancelled for the second day in a row after protesters took over terminals.

The Qantas website lists flights to Australia initially due to leave on Tuesday as being scheduled for Wednesday morning departures.

Veteran ABC reporter and journalism academic Monica Attard posted photographs of student protesters returning to the airport just before 5pm AEST.

"Dozens of flights being cancelled again," she tweeted.

Mr Morrison earlier described the situation as "very, very serious" and urged Hong Kong's political leaders to de-escalate the situation and listen "carefully to what people are saying".

There are mounting fears China may be about to ramp up its response to ongoing mass rallies.

Beijing has accused protesters of "serious crimes with sprouts of terrorism emerging" and says the situation amounts to an "existential threat".

"One must take resolute action toward this violent criminality, showing no leniency or mercy," Hong Kong and Macao Affairs Office spokesman Yang Guang said from Beijing.

Some legal experts have warned the use of the term 'terrorism' could see extensive anti-terror powers invoked.

Mr Morrison has stopped short of telling Australians not to travel to Hong Kong, but rejected China's characterisation of the protests as nascent terrorism.

"That's certainly not the rhetoric that I would certainly use to describe those events," he said in Sydney.

"Of course we're concerned, particularly because of the number of Australians, residents and citizens in Hong Kong both on a long-term basis and on a short-term basis."

There are reports China's People's Armed Police, which is used to deal with riots and terror attacks, have assembled for exercises in Shenzhen, which links Hong Kong to China's mainland.

Malcolm Jones was returning to Melbourne from Vietnam via Hong Kong when he and his wife got caught up in the chaos on Monday.

They went to the Qantas lounge, listening to the protest action playing out around them, but were soon told all flights had been cancelled until further notice.

Mr Jones expressed support for the protesters, telling the ABC: "Hong Kong citizens are really protesting about what is going on in their country ... and we all have empathy for that."