Experts have called for better airport security checks and harsher punishment for people who make false threats after hoax calls to airlines delayed two flights and forced another to make an emergency landing this week.

Two Air China flights received threatening phone calls before takeoff on Tuesday, the flagship carrier said in a statement posted on its official account on micro-blogging site Sina Weibo.

The flights, CA4111, from Lhasa to Beijing, and CA1578, flying from Nanchang to Beijing, were threatened in phone calls from unidentified people. The calls prompted the planes to undergo strict checks according to civil aviation management regulations, the announcement said.