All flights in and out of Hong Kong were cancelled on Monday after thousands of protesters flooded the city's airport to denounce police violence.

The abrupt shutdown at one of the world's busiest hubs came as the Chinese government signalled its rising anger, denouncing some of the violent demonstrations as “terrorism”.

The developments marked yet another dramatic escalation in a 10-week crisis that had already become the biggest challenge to Chinese rule of Hong Kong since the 1997 British handover.

A crowd of protesters that authorities said numbered more than 5,000 descended on Hong Kong airport on Monday carrying placards and chanting slogans denouncing police violence at previous rallies.

Although other rallies had been held over the previous three days, the airport authority said Monday's one had caused significant chaos.

“Airport operations at Hong Kong International Airport have been seriously disrupted as a result of the public assembly at the airport today,” it said in a statement.

“Other than the departure flights that have completed the check-in process and the arrival flights that are already heading to Hong Kong, all other flights have been cancelled for the rest of today.”

It warned that traffic to the airport was “very congested” and the facility's car parks were completely full.

“Members of the public are advised not to come to the airport.”

At the airport, protesters held signs reading “Hong Kong is not safe” and “Shame on police”.

They were responding to allegations that police were using increasingly violent tactics to suppress protests.

Over the weekend police fired tear gas into subway stations.

Protesters were also enraged at police apparently dressing in the black T-shirts worn by the protest movement to infiltrate rallies and make surprise and violent arrests.

Protesters responded on the weekend by hurling bricks and spraying riot police with fire extinguishers and water hoses.

A government official said 45 people were injured in the clashes, including two who were in serious condition.

Among them was a woman who suffered a serious face injury, reportedly after being hit by a bean bag round, with rumours circulating that she had lost her vision in the incident.

Images of her lying on the ground with blood pouring from her face quickly went viral and featured on posters calling for new demonstrations.

It was the 10th consecutive weekend that protesters have taken to the streets in a movement that began over opposition to a bill allowing extradition to mainland China.

The protests have morphed into a broader bid to reverse a slide of democratic freedoms in the southern Chinese city.

In Beijing, authorities slammed violent protesters who had thrown petrol bombs at police officers and linked them to “terrorism”.

“Hong Kong's radical demonstrators have repeatedly used extremely dangerous tools to attack police officers, which already constitutes a serious violent crime, and also shows the first signs of terrorism emerging,” said Yang Guang, spokesman for the Hong Kong and Macao Affairs Office of the State Council.

“This wantonly tramples on Hong Kong's rule of law and social order. “