Emergency services have been called to the seafront in Essex to investigate reports of people coughing and struggling to breathe.

Police, the ambulance service and the fire service attended Fourth Avenue in Frinton, off the Esplanade, after receiving calls from beachgoers in distress shortly after 2pm on Sunday.

Tendring district council later tweeted that Clacton, five miles down the coast, had also been affected, and coastal patrol advised people in both locations to get out of the water.

A spokeswoman for East of England ambulance service said it had received “reports of a large number of people suffering from coughing on the seafront in Frinton and Clacton”.

“The cause for this is currently unknown and we and our partner agencies are working to try and establish the cause as quickly as possible,” she said. While we are doing this, we are advising people to not go into the sea.”

She said patients had found their symptoms had improved after coming out of the water. Those affected were advised to wash after leaving the sea, change clothing and drink fresh water, and to call NHS 111 if their symptoms persisted.

Speculation about a fuel spill surfaced on social media, but this was not confirmed by police or ambulance services. Several people said they had been told by what appeared to be coastguards that a spillage might have been the cause.

A mother who was on a family day out said one of her children was left gasping for breath. Miriam Lansdell, 45, from Derbyshire, was visiting the beach in Frinton with her 10-year-old twin daughters, her parents and her husband.

“Just before 3 o’clock I started feeling unable to breathe, and thought I was having an asthma attack. Then my daughter started having rapid, shallow breathing and started crying. She said she had a burning sensation in her chest and throat when she inhaled. That’s when I thought: ‘We need to get out of here’.”

Facebook Twitter Pinterest Officials in a dinghy warn people to get out of the water. Photograph: Mark Wray/PA

Lansdell said her father was told to get out of the water by a man on a jetski who appeared to be a coastguard. Her daughter was given an inhaler at a walk-in clinic and is now doing OK. “We all have a bit of a residual cough,” Lansdell said.

Mark Fry said on Twitter: “I was there from 10am-2pm and left with definite breathing problems. I’m slightly asthmatic. There was a haze in the air. My lung capacity feels almost back to normal four hours later, but it’s still concerning.”

Another man, tweeting under a pseudonym, said he and his two children suffered a “coughing attack after going in the water”. “After a short time in the water both of my children developed a severe cough. Many other children coughing and some being sick,” he wrote.

In August 2017, a major incident was declared when more than 50 holidaymakers fell ill after inhaling toxic fumes from a yellow fog that appeared over Birling Gap in East Sussex. Various witnesses reported at the time that the fumes smelt like chlorine, ammonia and burning plastic.