Staff at a chemicals factory in north-western France are working to stop a gas leak that has spread a foul smell to Paris and south-east England.
French Ecology Minister Delphine Batho said she was heading for Rouen, where the factory is located, to oversee operations to deal with the leak.
Thousands of people, from as far away as Paris and London, have complained of nausea and headaches.
A stinking cloud of gas has been hanging over large areas of England after a leak at a French chemical plant, sparking thousands of calls to emergency services.
The sulphurous stench – likened to rotten eggs – is said by officials to be completely harmless.
But police in Kent, Sussex and Surrey began to receive floods of calls from concerned residents on Tuesday morning – and by afternoon there were reports of the unwelcome whiff in Oxfordshire and as far north as Northampton.
The gas, called mercaptan, was accidentally leaked from a factory in the northern city of Rouen and before long had drifted over the English channel.