The Fire Brigade Union are walking out for the second time in a week due to rows over pensions. The government wants firefighters to work until they are 60.
Fire departments across Wales have issued safety warnings in light of bonfire night and are asking people to be careful with fireworks.
Trained auxiliary firefighters will step in to cover duty during the industrial action. The FBU will picket from 06:00 and 08:00 this morning.
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A group of ex-servicemen have become the first people to climb Pen y Fan in the Brecon Beacons for 24 hours non-stop.
Thousands of athletes are in Tenby for the competition which consists of a two mile swim, a 112 mile cycle ride and a marathon.