Kent villagers were rocked by a huge noise today - a six-horn siren built to warn villagers of a potential disaster.

The 30ft gas leak warning siren was tested from 11am today on the Isle of Grain - only the second time it has been set off.

It was first used three years ago, amid fears there were not enough safety procedures for Grain LNG, a £1 billion gas import terminal.

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The siren will only ever be used "in anger" if there is an emergency at the terminal, which provides a fifth of the UK's gas.

If it sounds, residents are advised to go indoors, shut their windows and listen to the radio.

A statement has been released from Medway council, which is responsible under hazard regulations for producing an off-site emergency plan.

It is a requirement that the emergency plans - both on and off-site - be tested once every three years.

Video: Locals react to the siren

A major accident is described as "an occurrence (including in particular, a major emission, fire or explosion) resulting from uncontrolled developments in the course of the operation of any establishment and leading to serious danger to human health or the environment, immediate or delayed, inside or outside the establishment and involving one or more dangerous substances."

The Grain village siren will be set off between 11am and 12.30pm today, and may be heard across Medway, including Chatham and Gillingham.

There will be four alarms lasting two minutes each.

There are two different siren tones: on hearing the first alert people should "go in, stay in, and tune in".

A different tone will sound the all-clear. This will mean the incident is contained and any leak of LNG stopped.