Hong Kong International Airport has cancelled all departures for the remainder of the day Monday, halting operations in one of the busiest terminals in the world as protesters demonstrated here for the fourth day.

All flights not yet checked in by Monday afternoon were cancelled. In a statement, the airport authority cited serious disruption by protests as around 5,000 anti-government protesters have been staging a demonstration at the airport.

Hong Kong police claimed that some of the activists had moved to the departure area of the airport, causing disruptions, but declined to comment if it would move to clear the protesters. 

The airport authority advised all passengers to leave the terminal building as soon as possible. It also advised the public not to come to the airport. 

The authority also said that roads to the airport were very congested and car park spaces were full.

“Other than departure flights that have completed the check- in process and the arrival flights already heading to Hong Kong, all other flights have been canceled for the rest of today,” the airport authority said in a statement, as cited by Reuters.

Hong Kong's flag carrier Cathay Pacific urged its customers to postpone non-essential travel and advised them not to proceed to the airport. The cancellation period for the Hong Kong flights will last until Tuesday morning. 

On Saturday, Cathay Pacific also said it suspended a pilot who was arrested during one of the anti-government protests in Hong Kong and warned that overly radical staff would not be allowed to crew flights to the mainland

“Cathay Pacific Group employees who support or take part in illegal protests, violent actions, or overly radical behavior shall be immediately suspended from any activity involving flights to the mainland,”  Cathay Pacific CEO Rupert Hogg said.

The Asian financial hub is experiencing its most serious crisis in decades amid street protests. Mass demonstrations began in June in opposition to a bill that would allow extradition to mainland China. The rallies have since snowballed into a democracy movement, with some calling for full autonomy from Beijing. 

Hong Kong, a former British colony, was returned to Chinese rule in 1997, but it was granted semi-autonomy and a separate legal system for 50 years.