The Welsh Ambulance Service saw a 170% increase in calls over the first four hours of New Year's Day.
999 call handlers dealt with 721 calls between midnight and 04:00 GMT but they usually field an average of 267 calls in that time.
Wet weather led to slightly less demand for 999 callouts to public places, according to director of operations, Richard Lee.
New Year's Eve is the service's busiest night of the year.
Ambulances were deployed to 305 callouts in the first four hours of 1 January but in 15 of those they found no one at the scene.
Medical advice was also given to 40 people over the phone.
Mr Lee said: "The early hours of 2018 were busy for our call takers. 140 calls were taken in first hour of New Year's Day.
"Our staff worked incredibly hard across Wales to provide care to some very ill patients as well as those with less serious conditions, many of whom we treated on scene or referred to other services."
People were urged to think twice before phoning for an ambulance on New Year's Eve after calls were made for colds and stomach ache over Christmas with 1,600 calls on Boxing Day - 300 more than usual.
Mr Lee added: "The health system is going to continue to be busy over the next few days as people begin returning to normal following the holiday period.
"We would advise people to choose well and remind them that the ambulance service and emergency departments are for life-threatening or serious injuries only."