Hong Kong's airport reopened Tuesday but its administrator warned that flight movements would still be affected, after China said widespread anti-government protests that halted flights a day earlier showed "sprouts of terrorism."

The notice was published on the Hong Kong International Airport's official mobile app at 6 a.m. local time. The airport, one of the world's busiest, blamed demonstrators for halting flights on Monday.

"Hong Kong International Airport will implement flight rescheduling today with flight movements expected to be affected," the notice said.

At least one Air Canada flight, which was scheduled to fly from Hong Kong to Vancouver, was affected by the Monday closure. The Tuesday flight was listed as "on time" on the airline's website.

"Customers are being rebooked on a replacement flight, AC2008, departing [Tuesday]," the airline told CBC News in a statement.

Other regular Air Canada routes between Hong Kong and Toronto have been unaffected so far by Monday's airport demonstration. But the impact on the ground was significant.

Hong Kong flag carrier Cathay Pacific said on its website that it had cancelled over 200 flights into and out of the airport on Tuesday.

Watch Hong Kong police demonstrate a water cannon:

Hong Kong police demonstrated an anti-riot water cannon in a warning to protesters as authorities toughen their approach to the ongoing demonstrations. 0:37

The exact cause for Monday's airport closure was not clear as protesters occupying the arrivals hall for the past five days have been peaceful. Most had left shortly after midnight, with about 50 protesters still there on Tuesday morning.

The increasingly violent protests have plunged Chinese-ruled Hong Kong into its most serious crisis in decades and presented a serious challenge to Beijing.

Embattled Hong Kong Chief Executive Carrie Lam said on Tuesday the "lawbreaking activities in the name of freedom" were damaging the rule of law and that it could take a long time for the city to recover from the protests.

The protesters have been switching tactics in recent weeks and more than a dozen sit-ins were planned at hospitals in the city, according to social media posts on Tuesday.

Hong Kong's Airport Authority cancelled all flights not yet checked in by Monday afternoon because of anti-government protests, the agency said. (Tyrone Siu/Reuters)

Prime Minister Justin Trudeau said Monday he is very worried about events in Hong Kong, which has a large Canadian population, and urged Chinese authorities to handle the protests with tact.

"We are extremely concerned about the situation in Hong Kong. We see the need for de-escalation of tensions, we need to see the local authorities listening to the very serious concerns brought forward by Chinese citizens," Trudeau told reporters in Toronto.

"We are calling for peace, for order, for dialogue.... 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 said.

Canada is locked in a trade and diplomatic dispute with Beijing.

In Beijing, the cabinet's Hong Kong and Macao Affairs Office issued a statement saying the situation in Hong Kong was "beginning to show the sprouts of terrorism" and constituted an "existential threat" to the population of Hong Kong.

Some Hong Kong legal experts say the official description of terrorism could lead to the use of anti-terror laws.

Demonstrations began earlier this year in response to an extradition bill that would allow Hong Kong authorities to send people to China to face charges. The bill has been scrapped, but protests have continued as demonstrators accuse China of encroaching on Hong Kong's political autonomy.



Last week, Canada increased its travel advisory for Hong Kong due to the protests, telling travellers to exercise "a high degree of caution." The move came after the U.S. and Australia made similar updates to their travel alerts; Ireland, Britain and Japan have also issued travel advisories to their citizens.