A drink-driver nine months pregnant was among those caught in a transtasman blitz on alcohol and violence at the weekend.

The 20-year-old registered a breath-alcohol level more than twice the permitted limit, and Sergeant Ray Wylie of the Eastern Bay of Plenty strategic traffic unit says Child, Youth and Family has been told about her.

Mr Wylie said he was concerned by the number of women being processed and their high levels of breath-alcohol.

Up to 100 people were arrested in two New Zealand city centres as part of the crackdown.

Police on both sides of the Ditch were out in force on Friday and Saturday for Operation Unite, the first joint operation of its type between the two countries.

The blitz focused on people getting drunk at home and then going out on the town.

In Tauranga, Senior Sergeant Glenn Saunders said there were 49 arrests for crimes attributed to alcohol.

Offences ranged from disorderly behaviour to using obscene language.

In Christchurch, Senior Sergeant Kerry Joyce said 50 arrests were made over 24 hours, which was not unusual.

"We've had a very high police presence, which has definitely lessened people's silliness with alcohol."

The Canterbury area commander, Inspector Derek Erasmus, said officers targeted low-level offending relating to alcohol in the central city before it could escalate. "This removed a significant number of the instigators of serious crime early on."

Police in Auckland and Wellington were unable to detail how the operation went. It is understood the full impact of the crackdown will be released today with nationwide statistics on arrests.

Hastings police said the operation had been very successful. Napier police said a few arrests were made for drunkenness and disorder, but no more than expected.

In Invercargill, Senior Sergeant Dave Kirby said there had been about half the normal number of arrests for a weekend, and in Dunedin, Senior Sergeant Bruce Ross said it had been a typical Saturday night.

Alcohol-related crime costs New Zealand $1.1 billion and Australia $2.14 billion annually. In New Zealand, a third of crimes in 2007-2008 were carried out by someone affected by alcohol and in serious offences, such as homicides, it was about half of cases.

Every year police take 21,000 drunk people home, or to the cells because they cannot remember where they live.

Police in both countries said they were fed up with the dangerous binge- drinking culture.

"We expect high spirits as people take advantage of the summer festivities, but year on year there are those that take it too far, drink excessively and make very poor decisions," said North Island central district operations manager Inspector David White. "We won't be just standing back and letting this happen."