Investigations are continuing to try to find the cause of a toxic mist that enveloped part of the Sussex coastline on Sunday.
Holidaymakers were evacuated from the beach and at least 150 people needed treatment when the "haze" rolled in along the coastline.
People on Birling Gap beach in East Sussex were left with streaming eyes, sore throats and vomiting after a suspected chlorine leak.
Coastguard rescue teams from Birling Gap, Eastbourne, Bexhill and Newhaven raced to help clear the busy beaches, while people were warned to keep their doors and windows closed.
Eyewitnesses reported seeing a "foggy haze" rolling in "off the sea out of nowhere" before people started suffering from various symptoms.
The cause remains a mystery, but it is not thought the incident was caused by pollution from France.
East Sussex Fire and Rescue Service said they were treating it as a "chemical incident".
Sussex police said "hundreds" were thought to have been affected by the toxic cloud on Saturday evening.
"Long queues built up at Eastbourne General District Hospital well into the evening, with approximately 150 people being treated," it said.
"Initially, patients were dealt with as a precaution with a full decontamination treatment, but it became clear that this was not necessary following clinical advice."
It said effects were "mostly minor" and no one was admitted into hospital.
One holidaymaker described people rubbing their eyes and coughing in "all sorts of strange behaviour".
Kyle Crickmore said: "Then looking out towards the water, there was just this crazy foggy haze rolling in off the sea out of nowhere.
"It was definitely out of the ordinary considering it was a nice clear sunny day 10 minutes beforehand.
"It was stupidly busy and it was a boiling hot day. It emptied in about 10 minutes which was quite staggering considering the amount of people who were there."
Fire services said on Sunday that they had stopped dealing with calls and the cloud appeared to have cleared.
But authorities are still struggling to work out the source of the haze.
Sussex police said: "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,although it does appear that it did sweep in from the sea driven by on-shore breezes.
"However, weather models suggest that an onshore source in northern France is very unlikely."
Bob Jefferey, of the Royal National Lifeboat Institution (RNLI) Eastbourne division, said it would be business as usual on Monday, with thousands expected to flock to the coast for the Bank Holiday.
He said: "Whatever it was, it smelled like burnt plastic. It hung about and didn't move yesterday because there was no wind. The cloud seems to have dispersed today though.
"The hospital has downgraded the threat to pretty much non-existent now."