Garda Commissioner Drew Harris said gardaí have "changed their approach" at airport checkpoints following reports that people were booking dental appointments in Tenerife to avoid being fined for non-essential travel.
"From this morning, we warn people that we do not regard a dentist's appointment as a reasonable excuse to travel and that they may be prosecuted if they carry on with their journey."
Speaking on the Late Late Show, he said the €500 fine was not the deterrent they thought it might be but "today we found that people have turned back rather than be prosecuted and risk imprisonment or a suspended sentence".
Commissioner Harris also spoke of his own battle with coronavirus over Christmas. "I was back to work after about two and a half weeks. I was lucky to get the milder version but it was no joke."
He said the murder of his RUC officer father, Alwyn Harris, by the IRA in 1989, had a "profound effect" on his outlook.
He had "worked hard at not being bitter" and said the tragedy left him with "an empathy for those who have been the victims of serious crime".
Earlier, it was revealed that more than 6,500 fines have been issued by gardaí for people in breach of Covid-19 restrictions, with over 4,900 of these issued for non-essential travel.
Up until close of business yesterday 6,550 fines were issued, with 4,911 of these being €100 fines issued for non-essential travel.
A total of 132 €500 fines for non-essential journeys to airports and ports were also issued, with the total number of €100 and €500 fines for this now in excess of 500.
Over 116 people have been fined €500 each for organising a house party, with 498 fines of €150 issued for attending house parties.
A further 127 fines of €80 each have been issued to people not wearing face coverings.
Gardaí have said that for the first three days of this week - when fines for non-essential cross-border travel came into operation - data shows that traffic volumes in border areas was down 13% on last week.
They have said the number of fines for cross-border travel is currently being collated.
Gardaí have also said that over the last few days, they have attended breaches of restrictions at licensed premises, restaurants, retail outlets, and hair and beauty salons, and that in all instances, files will be forwarded to the DPP.
Prosecutions are being taken against three retail premises, while 95 are being taken against licenced premises. Forty-four of these currently have court dates.
Speaking today, Deputy Commissioner John Twomey said the vast majority of people "are doing the right things".
"They are staying home. Making only essential journeys. Limiting their contacts. We know it is hard. We know it has meant huge sacrifices. We thank them for this and ask people to continue to do the right things," he said.
He added: "Unfortunately, there are still people in this society who are prepared to put themselves, their families, their friends and their colleagues at risk of getting Covid-19. Everybody in this society has an individual and collective responsibility to play their part in reducing the spread.
"Everybody in this society has an individual and collective responsibility to play their part in saving lives and reducing serious illness. It is long past time for those who are not playing their part to do so."
Gardaí have said nationwide checkpoints and high visibility patrols across the country will also continue this weekend, and have again advised the public of the need to plan their activities over the weekend to take account that people are only allowed to exercise within 5km of their home.
