Portuguese airport security workers went on strike on Friday, forcing cancellation of some flights at smaller airports, union and airport officials said.

The Aviation Workers Union launched the 24 hour strike at midnight (0000 GMT) in a dispute over job security. The union accuses the government's National Airport Authority (ANA) of wanting to replace its members with outside firms.

More than half of all flights at Oporto, Faro in the Algarve tourism region and in the Azores islands were cancelled because of the strike, ANA spokesman Rui Oliveira told TSF radio.

Lisbon's Portela Airport, Portugal's biggest, and airports on Madeira island were unaffected by the strike.

A union spokesman said only three of 13 arriving flights had landed at Oporto by 8:30 a.m. and only one of 15 departing planes had taken off, Lusa news agency reported.