China ramped up the rhetoric against Hong Kong protesters, saying they “acted like terrorists” while swarming the city’s airport, as authorities restricted terminal access in a bid to stave off further demonstrations.

Service on Airport Express trains will be adjusted to run at 25-minute intervals instead of the usual 10, and only departing passengers with a ticket or boarding pass for a flight in the next 24 hours will be eligible to enter terminal buildings, Hong Kong’s Airport Authority said Wednesday afternoon. It urged passengers to arrive three hours early.

Small pockets of protesters remained at the airport, which resumed normal operations after a chaotic night of protest in which demonstrators beat and detained two suspected infiltrators and President Donald Trump warned of Chinese troops massing on the border. The Airport Authority said it had obtained a court order to bar people from “unlawfully and willfully” obstructing airport operations.

“These atrocities, which are lawless, trampling on human rights and inhumane, have completely gone beyond the bottom line of civil society, and is no different to terrorists,” China’s Liaison Office in Hong Kong said in a statement on Wednesday. In a separate statement, the State Council’s Hong Kong and Macau Affairs Office strongly condemned the “almost-terrorism behavior” of the protesters and called on them to be severely punished.

The comments come as fears grow that China may either mobilize troops or take other actions against protesters after they brought air traffic to a halt over the past two days, furthering the economic damage to Asia’s financial capital during protests that have raged on since June. The demonstrators, who initially hit the streets to oppose a bill allowing extraditions to the mainland, now have a host of other demands including the resignation of Hong Kong leader Carrie Lam.

The images of riot police clashing with protesters at the airport further dented Hong Kong’s reputation as a stable place to do business during the 11th week of protests against a bill allowing extraditions to China. The escalating stakes have raised fears that China would mobilize forces to restore order, a move that could scare away foreign companies and further erode the financial hub’s autonomy.

Trump stoked fears of a Chinese intervention, saying in a tweet that reports from U.S. intelligence agencies show mainland troops massing at the border with Hong Kong. He later told reporters that China is facing a “tough situation” in the city: “I hope nobody gets hurt. I hope nobody gets killed.”

A U.S. State Department official urged China to respect the agreements it made when taking control of Hong Kong from the U.K. and allow the city to “exercise a high degree of autonomy.” The statement—from an official who asked not to be identified—was the most forceful to date from the U.S.

At the airport, chaotic scenes emerged when protesters beat a man they accused of being a mainland police officer and then declined to let paramedics evacuate him from the scene. They eventually relented after police urged them to let the man go.

Afterwards, riot police briefly entered the airport after clashing with protesters who blocked roads to prevent officers from leaving the scene. Demonstrators then detained a second mainland Chinese man who turned out to be a reporter for the Global Times newspaper, which is published by the Communist Party. They tied him to a luggage trolley before allowing paramedics to evacuate him.