United States, Canada warn China over Hong Kong

Departures from Hong Kong's airport will reportedly restart on Tuesday after flights were cancelled on Monday evening amid protests.

A spokesperson for the airport told CNN that flights will resume at 10am (NZ Time). They were cancelled on Monday night after anti-Beijing protesters conducted a large sit-in in the airport, disrupting operations.

The airport is hoping to give travellers certainty over their flights. It is using a rescheduling system to adjust flight times, but admits some will be cancelled.

"Some of the flights will be canceled and some will be delayed. This will give passengers the opportunity to know whether their flights are going to fly or not," CNN was told.

Earlier on Tuesday, US Senate Republican leader Mitch McConnell warned China that any violent crackdown on protests in Hong Kong would be "completely unacceptable".

"The people of Hong Kong are bravely standing up to the Chinese Communist Party as Beijing tries to encroach on their autonomy and freedom," McConnell wrote in tweet on Monday.

"Any violent crackdown would be completely unacceptable ... The world is watching."

Canadian Prime Minister Justin Trudeau said he was extremely concerned about events in Hong Kong and urged Chinese authorities to handle the protests there with tact.

"We certainly call on China to be very careful and very respectful in how it deals with people who have legitimate concerns in Hong Kong," Trudeau told a news conference in Toronto on Monday.

Increasingly violent demonstrations in Hong Kong have plunged the Chinese-ruled territory into its most serious crisis in decades, presenting Chinese leader Xi Jinping with one of his biggest popular challenges and raising fears of direct intervention by Beijing.

Some Hong Kong legal experts say official descriptions of some protesters' actions as terrorism could lead to the use of extensive anti-terror laws and powers against them.

China's People's Armed Police have assembled in the neighbouring city of Shenzhen for exercises, the Chinese state-backed Global Times newspaper said.

US President Donald Trump, who has been seeking a major deal to correct trade imbalances with China, drew criticism this month after he described the Hong Kong protests as "riots" and said they were a matter for China and Hong Kong to deal with as the territory was part of China.

On Monday a senior Trump administration official and a State Department spokeswoman urged all sides to refrain from violence, while stressing support for democracy.

The senior official reiterated Trump's remark that it was a matter between Hong Kong and China, "with the understanding that 'they're looking for democracy and I think most people want democracy'.

"Societies are best served when diverse political views are respected and can be freely and peacefully expressed. The United States urges all sides to refrain from violence," the official said, speaking on condition of anonymity.

A State Department spokeswoman repeated calls for Beijing to adhere to its commitments to allow Hong Kong a high degree of autonomy after its 1997 handover from British rule.

She said it was important for the Hong Kong government to respect freedoms of speech and assembly

"We condemn violence and urge all sides to exercise restraint, but remain staunch in our support for freedom of expression and freedom of peaceful assembly in Hong Kong," she said.

"The ongoing demonstrations in Hong Kong reflect the sentiment of Hongkongers and their broad concerns about the erosion of Hong Kong's autonomy," she added.

"Freedoms of expression and peaceful assembly are core values that we share with Hong Kong; these freedoms must be vigorously protected."

A spokesman for British Prime Minister Boris Johnson said on Monday that Britain was concerned about the latest violence in Hong Kong and called for calm from all sides.