Hong Kong International Airport cancelled all flights after thousands of pro-democracy protesters filled its main terminal on Monday. The airport’s website advised all passengers to leave the building. It said that the demonstration “seriously disrupted” airport operations. China’s central government is closely watching developments in Hong Kong. The government described the largely leaderless pro-democracy movement as something close to “terrorism.” The airport demonstration followed unrest Sunday night in the former British territory. Protesters blocked roads and ignored police orders to leave early Monday after riot police used tear gas and rubber bullets to clear away crowds. Many people were reported injured in several areas.