People are being reminded the coronavirus lockdown rules do not allow overnight camping at beauty spots.
The warning comes after police woke up people in campervans in Newquay, Cornwall and officers in Dorset found a group camping on a beach in a gazebo.
Devon and Cornwall Police and Crime Commissioner Alison Hernandez said the force did not want people coming to the South West for sleepovers.
But she said the reality was police were fighting a “losing battle”.
Ms Hernandez said beaches and beauty spots in Devon and Cornwall had been “inundated” with campervans, caravans and day trippers but she said no public toilets were open and many car parks were closed, causing people to park illegally.
“We are worried going into the bank holiday weekend that people are not heeding the advice about staying home,” she said.
She added that the government guidance was that people should spend the night at their primary residence, and pointed out that there is only one hospital in Cornwall.
On Thursday Newquay police said officers had been out on dawn patrol, waking up people who had stayed overnight in vehicles.
In nearby Perranporth, residents took to social media to share pictures of campervans in a clifftop car park and of tents on the beach early in the morning.
Truro and Falmouth MP Cherilyn Mackrory said she had spoken to the Prime Minister’s Office, as well as local police.
“Earlier today it was brought to my attention that there were a number of caravans and campervans that were parked up and stayed overnight last night on the north coast – particularly in Perranporth,” she said.
“Let me be clear, this is not on.”
Mrs Mackrory said the behaviour of those who chose to break the rules regarding overnight stays was “irresponsible and dangerous” and “risks the health and wellbeing of our coastal communities with a second peak of Covid-19”.
In Dorset on Thursday, police patrolling Sandbanks beach near Poole said they spoke to a group of people from London who had camped overnight in a gazebo.
Councillor Laura Miller, who represents the area of Dorset that includes Durdle Door and Lulworth Cove said people had been sleeping in their cars and urinating in gardens.
And on Thursday night, the coastguard and police were called out after a man from London pitched two tents “around one foot” from the cliff edge, she said, adding that it was “so dangerous”.
Nick Lomas, the Caravan and Motorhome Club’s director general, pointed out that many motorhome owners would be using their vehicles legitimately.
He said: “As a responsible members’ club, we actively encourage members to adhere to rules and guidelines.
“Many people have a motorhome/campervan as their only vehicle and will sometimes need to use it for trips to the shops and if travelling for exercise.
“Neither of these groups are breaking the current regulations and we are sure the public will recognise this.”