Beach-goers in Dorset were urged to "head home" as resorts and car parks in some areas filled up on Friday.
A mobile app to aid social distancing was showing red along four areas of the coast - including at Sandbanks and Bournemouth West - meaning "avoid".
Police and the county's councils urged people to "enjoy Dorset safely this weekend" ahead of expected high temperatures of 27C (80F).
Council officers, as well as police, have been patrolling some seafronts.
A joint statement from emergency services, Dorset Council, Bournemouth, Christchurch and Poole (BCP) Council and the NHS, said "evidence gathered" over recent weeks had shown "people are using their common sense and are leaving places which feel too busy to be socially distanced from other people".
BCP Council recently launched an app to show potential visitors the "hot spots" along a seven-mile stretch between Poole Harbour and Highcliffe.
The authority said the app had already been downloaded more than 24,000 times, with a further 4,000 downloads expected over the weekend.
There have also been requests for it to be made available for other beaches across the UK.
In Sandbanks, where sun-seekers gathered in their droves last week, a "head home" sign was illuminated by about 10:30 BST on Friday alongside a "car park full" notice.
Dorset Council said it was "monitoring the situation closely" and had "robust plans in place to manage the anticipated high numbers of visitors".
It said its beaches were "filling up" early but added there had been no reported issues.
A spokeswoman said extra parking enforcement staff had been deployed to the coast, with Durdle Door car park reaching capacity and visitors urged to "go elsewhere".
Train services between Bournemouth and Southampton were also "much busier than normal", according to South Western Railway and BCP Council.
Clare Franklin, 45, has travelled from Tamworth, Staffordshire, with her 46-year-old partner Simon Paterson.
She said she did not believe people were doing anything wrong by visiting the beach.
"We've just walked the length of the beach from Bournemouth to Poole and everyone seems to be adhering to the rules," she said.
"I think sometimes the photos you see in the media can make it look a lot worse than it is."
Sam Rogers from Poole said she also felt most people were respecting social distancing rules but was worried about litter.
The mother-of-three said her children had picked up 210 beer bottle tops from the beach last week.
"Since lockdown everyone has been holidaying at home so much more - and the busyness at the beach is stoked by the tabloids saying how much of a scorcher it's going to be."
Dorset Police said there had been no reported incidents relating to the weather, but urged visitors to take their litter home with them.
A spokeswoman added: "As part of our usual summer policing plans, we have extra patrols and resources on throughout the summer."
The Met Office said Dorset, as well as other areas of the south and south-west of England, would likely experience a heatwave "early next week".
At the scene: Toby Wadey, BBC South
It's deja vu here at Sandbanks - another scorching Friday, another packed beach.
The roads were again jammed with beach-going motorists, feverishly scrambling to get a space as the car parks swelled with sun-seekers.
But there's no doubting the influx of visitors hasn't yet reached the peak of recent weeks, with the council deploying traffic marshals and signs to tell the public to "go home" from early in the day.
In any other year the hoards of people might all seem quite unremarkable, but just six weeks ago BCP Council declared a "major incident" because of the crowds.
There's no doubt that, with an abundance of fluorescent jacket-wearing council staff out in force, officials are feeling cautious and it may be some time before a visit to the beach is the same again.
In Bournemouth, a major incident was declared on 25 June because of the crowds.
At the time police reported fights, overnight camping and three men were stabbed in an attack near Bournemouth pier.
Cars were left abandoned on verges as visitors struggled to park and the beaches were strewn with litter.
BCP Council now has powers to clamp or tow away vehicles parked illegally.