Hungarian police on Wednesday inspected all international trains entering the country after receiving an anonymous bomb threat, sparking major travel delays.

"An unidentified male called to say that he had placed a bomb on an international train traveling through Hungary," police said in a statement.

As many as 20,000 Hungarian and international travelers were affected by the delays lasting up to three hours, according to the national railway station company (MAV).

By Wednesday afternoon, more than 18 trains had already been searched before being allowed to continue their journeys, with no explosives found so far.

The checks will be carried out until midnight, MAV said.