Portuguese police have arrested two Australian nationals trying to smuggle rhino horns worth half a million dollars out of the country.

Authorities said Monday the two men were detained at Portugal's Lisbon airport after horns were found in their luggage.

The father and son had been booked on a flight to Ireland.

It was unclear if the horns were stolen from a natural history museum in the northern city of Coimbra, part of a recent rash of thefts of rhino horns from museums around Europe.

Rhino horns are highly valued in Asia, where it is believed they have powerful medicinal properties.