The annual exercise, co-ordinated by Norfolk Police, will take place on the morning of 19 August.

The sound will be a steady note for 30 seconds, then silence for 15 seconds, repeated for four minutes.

It comes as the Environment Agency predicted extremely high tides in September and October which could lead to flooding along the coast.

Flood imminent

In a real-life situation, the alarm would sound continuously with no breaks.

Chris Eldridge, operational planning manager for Norfolk Constabulary, said: "Areas of Norfolk can be at risk of flooding and it is vitally important that we ensure the existing flood siren systems are working correctly."

People living in coastal areas are also urged to register for the Environment Agency's Floodline system which gives warnings of flooding direct to people's homes.

The sirens are activated by police to advise the community it is time to evacuate because of an imminent flood.

The sirens are not used until it is time to go and, by the time they are heard, residents should have already received flood warnings through the media or from local flood wardens.