Hong Kong airport authorities cancelled all remaining departing and arriving flights at the major travel hub on Monday after thousands of protesters entered the arrivals hall to stage a demonstration.
"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," the airport authority said in a statement.
The decision came after thousands of pro-democracy demonstrators flooded into the airport holding signs reading "Hong Kong is not safe" and "Shame on police".
"Airport operations at Hong Kong International Airport have been seriously disrupted as a result of the public assembly at the airport today," the statement said.
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."
More than 5,000 protesters gathered at Hong Kong airport on Monday, police said, as authorities cancelled all the day's remaining flights in and out of the busy international transport hub.
"The information I got before we came in was that in the airport passenger terminal building there are over 5,000 protesters," said Kong Wing-cheung, senior superintendent of the police public relations branch, at a press conference.
Kong said airport authorities had allowed demonstrators to gather in the arrivals halls -- although the protest was not granted a permit from police -- but accused the activists of blocking departures.
"Some of the protesters had gone into the departures hall, causing some passengers to be unable to enter the restricted area to exercise their personal freedom, which is to board their flight," he said.
Pro-democracy activists staged three days of sit-ins at the airport from Friday, but the protests were significantly smaller than Monday's which followed a weekend of often violent confrontations between police and demonstrators across the city.
More than 5,000 protesters gathered at Hong Kong airport on Monday, police said.