A couple who travelled from Essex to Cardiff to deliver Christmas presents were among those caught breaching Covid rules through new police powers.
The powers follow concerns that groups of people from locked-down areas of the UK, where pubs and bars are closed, helped fill the streets of Cardiff city centre last weekend.
The Essex pair told officers they had driven almost 200 miles to drop presents off with family living in the capital.
A total of 110 vehicles were stopped by police in the first 24 hours of operation, which aims to ensure those visiting the city are doing so within the confines of coronavirus legislation.
South Wales Police said it has issued 12 people with fines since the powers came into force at 9am on Friday and end at 5pm on Sunday.
A further 15 people were told to leave Cardiff.
Officers also stopped a group of nine people who were travelling in convoy to visit friends at university.
Cardiff and Vale of Glamorgan Chief Superintendent Wendy Gunney, said: "I would like to thank the vast majority of people who are enjoying their weekend with caution and within the confines of the existing regulations, but those not adhering to the rules are continuing to put others at increased risk.
"The measures which are in place are in place for a reason. Our checks will continue throughout the weekend, and anybody blatantly flouting the rules, which have been made very clear, face being fined," she added.
Last weekend, some businesses in Cardiff said they were forced to close early because of large crowds in the area.
South Wales Police were also called to a number of incidents with numerous businesses warning of customers "not following Covid regulations".