People relax on the beach at Birling Gap in Eastboune, Sussex, England, on Monday, Aug. 28, 2017. More than 100 people have been treated for streaming eyes, sore throats and breathing problems after a chemical haze spread over a stretch of southern England coastline. (Gareth Fuller/PA via AP)

People relax on the beach at Birling Gap in Eastboune, Sussex, England, on Monday, Aug. 28, 2017. More than 100 people have been treated for streaming eyes, sore throats and breathing problems after a chemical haze spread over a stretch of southern England coastline. (Gareth Fuller/PA via AP)

LONDON (AP) — A mysterious chemical haze that left scores of people on the English coast with streaming eyes, sore throats and breathing problems has dissipated, but its cause remains a mystery, police and emergency services said Monday.

The gas cloud appeared Sunday, sending people fleeing from the beach and cliffs at Birling Gap, a popular coastal spot 60 miles (100 kilometers) south of London.

Life boats were dispatched to help clear people from the beaches there. Eastbourne District General Hospital said it had treated more than 130 people. Sussex Police said the injuries were mostly minor.

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“Whatever it was, it smelled like burnt plastic,” said Bob Jefferey of the Royal National Lifeboat Institution’s Eastbourne division. “It hung about and didn’t move yesterday because there was no wind. The cloud seems to have dispersed today, though.”

Pollution has been known to drift to Britain from industrial plants in France, but police said the wind direction made that unlikely in this case.

“Neither the gas nor its source have been established, but agencies are continuing to investigate and have not ruled out either on-shore or off-shore locations,” Sussex Police said.

Meteorological Office weather forecaster Jay Merrell said a ship in the English Channel may have been responsible, but stressed nothing conclusive had been proven yet.

Toxicologist John Hopkins said the haze might have been photochemical smog caused by sunshine reacting with vehicle pollution.

“It’s just a function of we’ve got too much traffic on the roads and too much sunshine,” he told Sky News.