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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Yellow and amber warnings of strong winds remain in place across Wales, as Storm Doris batters the UK.
Trees are being brought down by strong winds from storm Doris.
The 2017 Champions League final will be the biggest event ever held in Wales.