Families in south Kent are being asked to keep doors and windows closed after a gas cloud blew across from France.

The leak, believed to have drifted over from Rouen in north west France, has caused a strong sulphur-like odour to be wafted across the Channel.

It has spread across parts of Kent and East Sussex, and has led to callers flooding emergency numbers with reports of the pong.

But health experts have rushed to reassure people the smell is not a danger to the public.

A statement issued by the Health Protection Agency today said the odour, similar to rotten eggs, had been noticed by people mainly in Kent, East and West Sussex and some parts of Surrey.

It is caused by a particularly smelly chemical that is added to odourless natural gas to give that its characteristic smell.

The chemical leaked from a factory in Rouen, France yesterday and has blown across the Channel overnight.

A spokesman said: "It is not toxic and has also been diluted before entering the air over England, so people should be reassured it will cause no harm.

"It is an unpleasant odour which may cause some people to feel slightly nauseous, but it will dispel naturally.

The message was backed by LPG gas supplier Calor Gas.

The firm, which has a number of domestic and commercial customers in the south east, has had calls into its emergency line from concerned residents.

Stephen Rennie, managing director at Calor, said: "We have checked all of our storage facilities and can confirm no leaks are present.

"We are confident that any unusual smell of gas is a result of the leak in France."

Meanwhile, families as far afield as Maidstone and Ashford have been querying the all-pervading pong.

Folkestone Fire Station had around 30 calls from as far a Dover, Lydd and Ashford this morning from members of the public about the gas-like whiff.

A spokesman for Southern Gas Networks [SGN] also said it has had a number of reports from people in Ashford, Dover and Folkestone, who have had a whiff of an oil-like stink.

A report on the Kent Fire and Rescue Service website also attributed it to the French stink.

It urged people to close windows and doors to protect from the stink.

Folkestone crew manager Andy Batchelor said: “We received 30 calls between 6.30am and 8.50am.

“Transco believes there is a gas cloud sitting over south east Kent.

“Dover Coastguard have had reports from the French authorities saying there was a gas leak between Rouen and Paris.

“The prevailing winds have come from that area but it is not yet confirmed that the smell is from that source.”

Folkestone Fire Station had also received calls from Hythe, Dymchurch, Mersham and Charing.