Operations at Belgium's second-largest airport were briefly suspended on Tuesday due to a bomb alert on a Ryanair flight from Portugal, the company running the airport and the airline said.

Shortly before 11:00 am (0900 GMT) "a bomb threat was triggered" on board an aircraft that landed at Charleroi airport, said a spokesperson for its operator.

"A security perimeter was established around the aircraft," the spokeswoman said.

This required the runway to be closed as authorities took over, halting operations, she added. Air traffic eventually resumed at 1:45 pm.

Charleroi, south of Brussels, is a major European hub for low-cost airline Ryanair, which said the threat concerned one of its planes.

"Ryanair was informed of a security threat on flight FR6313 from Faro to Brussels Charleroi," the company said.

"Passengers have been disembarked and the aircraft is being prepared for return to service. We sincerely apologise to any passengers affected."

Belgian police did not immediately reply to a request for comment.