The police have urged drivers to be cautious on roads that are “wet and very, very busy” in the south west as lockdown restrictions are eased.
For the first time since March, people are allowed to stay overnight, with 80,000 visitors expected in Cornwall.
Pictures showed long queues of vehicles on the M5 including many camper vans and caravans.
Devon and Cornwall Police asked people to “keep a safe distance”.
There have also been a number of accidents in the region and heavy congestion near Exeter, according to Highways England.
Lorry driver Jason Leake posted pictures showing dozens of caravans in a car park at Taunton Deane Services on the M5 at 05:30.
“The volume of traffic including caravans overnight has been worse than a bank holiday,” he said, adding “Standby for the next #Lockdown”
Others raised concerns on social media the influx of visitors could increase the spread of coronavirus.
One local resident posted on Twitter: “Here were go, they descend upon my poor county of Cornwall, twice as many as normal and a lot more permanently closed shops.
“Who knows what these million holiday makers are bringing down with them and our single hospital.”
Toby Slade, associate medical director at the Royal Cornwall Hospital, said this was a “high risk time” for Cornwall as “coronavirus hasn’t gone away.”
Cornwall Council leader Julian German said he had been “incredibly impressed” with how hospitality businesses had been able to adapt to ensure they were safe to open for visitors and customers, but added that many places would remain closed.