People are watching a Cathay Pacific passenger plane land at Hong Kong's international airport. File photo/ AFP

Hong Kong’s Airport Authority has cancelled all flights not yet checked in by Monday afternoon, the agency said, as anti-government protesters peacefully demonstrated at the airport for a fourth day.

“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 cancelled for the rest of today,” the authority said in a statement.

Traffic on roads to the airport was very congested and car park spaces were full, the authority said.

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

Reuters