Calls for a mass protest at the airport came after police and demonstrators fought pitched battles on the streets across several districts of the city on Sunday.
"Protesters have been frequently using extremely unsafe tools to attack the police in recent days, constituting serious crimes with sprouts of terrorism emerging", Hong Kong and Macau Affairs office spokesman Yang Guang said in Beijing.
Lam said last month that the bill has failed but has refused to withdraw it completely, leading to accusations that she's simply stalling for another chance to ram it through.
"We are extremely concerned about the situation in Hong Kong".
Only flights that had already begun boarding or those cleared for landing were allowed to use runways at the airport.
"All other flights have been canceled for the rest of today", the airport statement said.
A massive traffic jam soon formed on the highway leading back to Hong Kong's city center.
Police are now attempting to remove protesters from the airport and there are long queues for any form of transport away from the airport.
Some Hong Kong legal experts say the official description of terrorism could lead to the use of anti-terror laws.
Protests have escalated over the past two months to the point of taking over the semi-autonomous Chinese city.
Protesters demonstrate at the airport in Hong Kong, Monday, Aug. 12, 2019.
Hong Kong protestors cripple airport But in recent years, some have accused the Communist Party-ruled central government of steadily chipping away at their freedoms. A journalist records evidence items presented by police at police headquarters in Hong Kong, south China, Aug. 12, 2019.
Police have also reported injuries among their ranks, including eye irritation from laser pointers, burns from petrol bombs and bruises and cuts from flying.
Over the weekend, protesters threw up barricades across the city as police fired tear gas into underground train stations and used bullets and pepper pellets at short range. Tear gas was sacked at crowds in the districts of Hong Kong, Kowloon and the New Territories.
Officers were also seen storming an enclosed railway station before firing tear gas inside and beating people with batons, sparking renewed allegations of brutality.
Earlier, a large group of mostly young protesters marched down the middle of Hennessey Road, a main shopping drag in the Causeway Bay area, as a rally was held in nearby Victoria Park. Dressed in the black T-shirts and dust masks that have become the de facto uniform of the protest movement, the visibly angry crowd chanted slogans such as "an eye for an eye!" - a reference to the young medic whose blood-drenched face became iconic overnight.
The post coincided with a statement from Chinese authorities vowing to crack down on Hong Kong protesters and likening the demonstrations to "terrorism". But in recent years, some have accused the Communist Party-ruled central government of steadily chipping away at their freedoms.
"I don't think I will ever fly to Hong Kong again", she said.
"They fight for Hong Kong and that's their view", he said.
Hong Kong's Airport Authority added that there were "calls online" for a public assembly in the airport on Tuesday afternoon.
"As violence increases, the more middle class people and ordinary people of Hong Kong will turn against this movement".
He said the protesters' "violent crimes" must be dealt with "resolutely" and "without mercy".