China warned Monday that increasingly violent protests in Hong Kong showed “signs of terrorism” and that Beijing was prepared to act. Yang Guang, a spokesman for the the Beijing government’s offices in Hong Kong and Macau, warned that attacks on police forces in Hong Kong would not be tolerated. “In recent days, Hong Kong’s radical protesters have repeatedly attacked police with highly dangerous tools, which constitute serious violent crimes and have started to show signs of terrorism,” Yang said. “This type of violent criminal activity must be resolutely combated according to the law, with no hesitation or mercy.” The stern warning came as Hong Kong airport authorities canceled all departures not already checked on Monday afternoon, stranding travelers and disrupting connecting flights at one of the busiest airports in the world. Inbound flights already en route will be allowed to land, but those scheduled to depart for Hong Kong could be canceled.