ATHENS, Greece —  Two airplanes were forced to circle an airport on a Greek island for 30 minutes Monday because an air traffic controller failed to show up for an early morning shift, authorities said.

Only one controller was on duty and ordered the two flights, one from Athens and one from Slovakia, to remain in a holding pattern over the island of Lesvos until airport officials found a replacement.

The aircraft had been due to land at Mytilene International Airport on Lesvos at 6:30 a.m (0330 GMT), an hour after the airport opened.

After the delay, they both landed safely, a Hellenic Civil Aviation Authority statement said. The agency said it was investigating.

The incident came to light when a passenger on the Olympic Airlines' flight 570 from Athens reported it to a private radio station, saying the captain announced to passengers that there was no controller at the airport.

A spokeswoman at Slovakia's main Bratislava Airport identified the second flight as Air Slovakia flight 2050.