[Here’s a guide to what prompted the Hong Kong protests and how they evolved.]

Members of the largely leaderless movement had called for the demonstration at the airport after a night of clashes on Sunday, during which the police fired tear gas inside one subway station and chased protesters down an escalator in another. Many airport protesters on Monday were angry that a woman at one of the Sunday demonstrations had been hit in her eye by a projectile.

“Yesterday’s escalation of violence and repression on the part of police, I think it’s a consequence of the very clear stance from Beijing that they are unconditionally behind the police and are relying on them to quell the protests in Hong Kong,” said Samson Yuen, an assistant professor of political science at Lingnan University in Hong Kong who studies local social movements.

As the clashes intensify, Chinese and Hong Kong officials are escalating their criticism of the protesters.

“Hong Kong’s radical demonstrators have repeatedly attacked police officers with extremely dangerous means,” said Yang Guang, a spokesman for the Hong Kong and Macau Affairs Office, which oversees Chinese policy toward the two cities. “These have already constituted serious violent crimes and have begun to show signs of terrorism.”