LONDON — A mysterious chemical haze that drifted onto England's south coast sent dozens to hospital on Sunday.

Around 150 people sought treatment complaining of eye and throat irritation while others vomited on clifftops around Birling Gap, which is located around 70 miles south of central London.

Public Health England said while those arriving at a local hospital initially received a full decontamination treatment, it soon became clear that wouldn’t be necessary.

An investigation has been launched to establish the source of the gas cloud. The area is less than 70 miles from the mainland European coastline.

Sussex Police said it appeared that the haze "did sweep in from the sea" but added that "weather models suggest that an onshore source in northern France is very unlikely."

Industrial sites in France have been blamed for similar clouds which reached England in the past.

The haze appeared to have largely dissipated by Monday morning.

Alastair Hay, a professor of environmental toxicology at the University of Leeds, said that authorities would be focusing on trying to identify what was in the cloud.

"The fact that it is relatively close to the ground suggests a heavier than air compound," he added.