Protesters clashed with police at the Hong Kong airport yesterday eve-ning, plunging the city into deeper turmoil after having forced a second day of mass flight cancellations.

Police said they responded after a visitor was besieged by a large group of protesters at the airport and assaulted, and that ambulance officers had been prevented from rendering medical assistance.

Protesters had detained at least two individuals they suspected of being spies or undercover officers at the airport yesterday, after police admitted on Monday that such officers were used in recent operations.

While flights had resumed early yesterday, the airport authorities said in the afternoon that all check-ins were suspended. Thousands of protesters had returned to the airport and conducted a mass sit-in.

Hong Kong leader Carrie Lam warned that protesters risked pushing the territory "into an abyss".