Beaches are becoming “unmanageable” due to large swathes of visitors, local authorities have warned, prompting fears around keeping people safe in the water.

The Coastguard had its busiest day for more than four years on Friday – when the UK recorded its third hottest day ever – as it dealt with more than 300 incidents.

Thanet District Council asked people to avoid four of the area’s beaches, including Margate’s Main Sands, due to the number of visitors.

Leader of the council Cllr Rick Everitt told the PA news agency: “Early on, it became clear that they were going to reach levels of which we were concerned about.”

Authorities expressed concern about keeping people safe in the water, as well as the potential spread of Covid-19 and maintaining social distancing.

“The RNLI only have a certain capacity,” Mr Everitt said.

“They’re on seven Thanet beaches this summer, which is slightly fewer than usual, and they’re doing a great job where they are but they don’t have unlimited resources to deal with people in the water.

“If you have too many people on the beach, it just becomes unmanageable from that point of view.”

Day trippers flocked to beaches across the country on Friday, sparking concerns about how sunseekers would keep to social-distancing measures.

Temperatures reached 37.8C (100F) at London’s Heathrow Airport at 2.41pm and also reached 37.3C (99.1F) at Kew Gardens, in west London, the Met Office said.

Many calls to the Coastguard on Friday were about people being cut off by the tide, missing children and swimmers getting into difficulty.

The Coastguard said the total number of UK incidents was 329, including 232 callouts for coastguard rescue teams, 129 for lifeboats, 22 requiring aircraft and three for a hovercraft.

The coast along Essex and Kent saw a total of 45 incidents, it added.

Mr Everitt said that Thanet’s beaches had seen “exceptional” numbers of visitors driven by the balmy conditions.

“We’re happy for people to come to Thanet, our economy is dependent on it, and obviously a lot of businesses in the coastal areas are struggling, because they missed so much of the season,” he told PA.

“So it is a bit of a balancing act for us, because we don’t want to be saying, ‘don’t come’, as we know small businesses around our seafront are desperate for the revenue.”

He said the facilities on the beaches, such as toilets, were not equipped for the number of tourists, while authorities would be able to cope better if demand was better distributed along the coastline.

“It’s an irony isn’t it that seaside towns have spent years complaining that people no longer visit them because they go abroad,” he added.

“We’re getting greater numbers than we’ve ever seen since package holidays became a thing.”

Large crowds and incidents of violence prompted South Wales Police to issue a dispersal order covering the Oval Basin in Cardiff Bay on Saturday.

A 27-year-old woman and a 23-year-old man were arrested on suspicion of assaulting an emergency worker after two officers were injured in separate incidents in the area on Friday night, according to the force.

The Maritime and Coastguard Agency (MCA) said a person was pulled from the water near Porthcurno, Cornwall, on Saturday afternoon.

Coastguard rescue teams, RNLI lifeboats, lifeguards, the coastguard helicopter, ambulance service and police responded after the person was reported in the water at 12.40pm.

“The person has been recovered from the water and transported to Porthcurno Beach for onward medical care,” an MCA spokeswoman said.

The Met Office said temperatures will be closer to average on Saturday, but it will still be pretty warm in the South East.

Met Office forecaster Simon Partridge said “the weekend is going to be pretty good”, and added: “Both days are going to be mostly dry across the UK with sunny spells and some showers at times that may be out to the north and the west of the country.”

Temperatures in the South East on Saturday could reach 26C or 27C and it could feel a little bit fresher with highs of 23C or 24C on Sunday.