Chinese civil aviation authorities plan to extend until June 30 their curbs on international flights to contain the spread of the coronavirus, the U.S. embassy in Beijing said in a travel advisory on Friday. China has drastically cut such flights since March to allay concerns over infections brought by arriving passengers. A so-called "Five One" policy allows mainland carriers to fly just one flight a week on one route to any country and foreign airlines to operate just one flight a week to China.