Police have been called out after more than 500 cars were lined up along roads in Snowdonia over the weekend.
Hundreds of drivers parked along Pen-y-Pass were issued with fines.
The national park authority said parking on roadsides can cause problems for farmers, local residents and emergency services.
Many of the official car parks were full over the weekend, with Pen-y-Pass car park already full by 8am on Monday.
It comes two weeks after the Welsh Government lifted the 'stay local' rule, allowing people in Wales to travel beyond five miles of their home.
A park warden made a desperate plea urging people to "avoid Pen-y-Pass at all costs" on Sunday.
They said: "It's getting very dangerous as cars and cyclist cannot pass safely.
"Social distancing is getting ignored, which makes this place a major health hazard in this current climate.
A councillor for Gwynedd Council described the scenes as "scary".
"Please, use some common sense. If your chosen car park is full, drive to another one, NOT park illegally on the road and make it dangerous," Cllr Nia Jeffreys said.
Officers have also issued a warning to visitors of the seaside town of Barmouth, Gwynedd, after the lifeboat station was partially blocked by parked motorbikes.
The RNLI crew at Barmouth said those parking in the boathouse forecourt were potentially putting lives at risk by preventing boats from launching easily.
Beauty spots in Wales have seen the number of visitors rise since lockdown restrictions were eased to allow long-distance travel.
North Wales Police received a number of complaints that large amounts of rubbish were left by families visiting the Great Orme.