French Ecology Minister Delphine Batho rushed back to France from Germany, where President François Hollande was meeting Chancellor Angela Merkel, to ensure that the leak was being dealt with safely, a ministerial statement said Tuesday afternoon.
Despite the official insistence that there was no danger, French social media were awash with people in the affected regions complaining of headaches and nausea.
Tuesday evening's French Cup tie match in Rouen between the city's football team and Marseille was postponed, the host club revealed.
"We didn't want to be in a situation where we have 10,000 spectators two kilometres away from the plant without any capacity for confining or evacuating them if that were necessary," said senior local official Florence Gouache.
Sussex police said the phones started ringing at 7.30am and that they received 25 calls in less than two hours, adding that police in the neighbouring county of Kent were also trying to calm olfactorily irritated householders.
Earlier residents of Paris had noticed the pong,
More than 10,000 people phoned fire and ambulance services overnight to complain.
The source was identified as a chemical factory outside Rouen, 110 kilometres west of the capital, which is part of US millionaire Warren Buffett’s business empire.
The smell came from a cloud of mercaptan, a non-toxic ingredient that is added to gas to alert people to leaks.
It contains sulphur and smells of sweat, garlic and rotten eggs, Paris police announced, adding that the smell was likely to hover over the city for “a good part of the day”.
“Its inhalation presents no risks,” they added.
The Rouen factory, owned by Lubrizol, which is owned by Buffett’s holding company, Berkshire Hathaway, manufactures the chemical and admits that some of it leaked out on Monday.
It has been struggling to “neutralise” the leak overnight and expects the operation to have finished during the course of Tuesday, Lubrizol said.