Four Western Bay of Plenty motorists have been tripped up by new drink drive limits after being caught and fined within the first week of the national rollout.

On Monday the current breath alcohol limit was reduced from 400mcg to 250mcg of alcohol per litre of breath for drivers over 20. The limit for those under 20 stays at zero.

Western Bay of Plenty Police at a roadside checkpoint. Photo: File.

The blood alcohol limit - reducing from 80mg to 50mg of alcohol per 100ml of blood - will bring New Zealand in line with the rest of the world.

Drivers caught between 251 and 400mcg receive an instant $200 fine, 50 demerit points and a ban from driving for 12 hours, but it will not result in a criminal conviction.

Western Bay of Plenty road policing manager Senior Sergeant Ian Campion is 'disappointed” that four motorists were caught over the new limits.

Ian says: 'I was hoping for a particularly high compliance rate given the publicity around it and the fact that 60 per cent of people out there wanted these changes.”

Three men and one woman were caught and fined, all blowing in the range of 300mcg of alcohol per litre of breath.

The first person was caught on Monday evening - the day the new law came into effect. Of the four, one motorist said they didn't know the new rules.

'They are people that simply haven't had a single drink and driven,” says Ian. 'They are drivers that have had a number of drinks prior to driving.”

'My message for people out there is if you are going to have a drink, don't drive.”

Ian says with Operation Profile in full swing the booze bus is out in the Western Bay every week meaning people can expect to be breath tested.

For the last five years, police have launched the operation from the end of October to around January 11, with the aim of getting alcohol or drug impaired drivers off the road.

The number of checkpoints are expected to increase as Christmas and New Year's Eve approaches.