Singapore is a major international transport hub in Asia, serving some of the busiest sea and air trade routes. Changi Airport is an aviation centre for Southeast Asia and a stopover on the Kangaroo Route between Sydney and London. There are three civilian airports in Singapore, Singapore Changi Airport, Seletar Airport and Kallang Airport (which is not open to public). Singapore Changi Airport hosts a network of over 100 airlines connecting Singapore to some 300 cities in about 70 countries and territories worldwide. It has been rated one of the best international airports by international travel magazines, including being rated as the world's best airport for the first time in 2006 by Skytrax. The national airline is Singapore Airlines. The Port of Singapore, managed by port operators PSA International and Jurong Port, was the world's second-busiest port in 2019 in terms of shipping tonnage handled, at 2.85 billion gross tons (GT), and in terms of containerised traffic, at 37.2 million twenty-foot equivalent units (TEUs). It is also the world's second-busiest, behind Shanghai, in terms of cargo tonnage with 626 million tons handled. In addition, the port is the world's busiest for transshipment traffic and the world's biggest ship refuelling centre.