Guangzhou is the capital and largest city of Guangdong province in southern China. Located on the Pearl River about 120 km (75 mi) north-northwest of Hong Kong and 145 km (90 mi) north of Macau, Guangzhou has a history of over 2,200 years and was a major terminus of the maritime Silk Road; it continues to serve as a major port and transportation hub as well as being one of China's three largest cities. For a long time, the only Chinese port accessible to most foreign traders, Guangzhou was captured by the British during the First Opium War. No longer enjoying a monopoly after the war, it lost trade to other ports such as Hong Kong and Shanghai, but continued to serve as a major transshipment port. Due to a high urban population and large volumes of port traffic, Guangzhou is classified as a Large-Port Megacity, the largest type of port-city in the world. Due to worldwide travel restrictions at the beginning of the COVID-19 pandemic, Guangzhou Baiyun International Airport, the major airport of Guangzhou, briefly became the world's busiest airport by passenger traffic in 2020.