Tougher sentences are not the answer to stopping assaults on police officers, say experts.

The police union's president says cracking down on insults commonly hurled at police would be the first step to ending assaults on officers, while a crime expert says a recent spate of violent attacks could have been spontaneous copycat crimes.

Both agree tougher sentences would have little effect.

Three officers have been attacked since Friday, when an off-duty officer in south Auckland was beaten unconscious by a group of youths after he tried to break up a fight.

On Saturday, an officer's lip was bitten off by a suspected drink driver near Whangarei. The constable was discharged from hospital after a successful surgery yesterday re-stitching his lower lip.

And last night, an Oamaru police officer was knocked to the ground and repeatedly kicked by a carload of people after the vehicle's driver failed a breath test. Three men between 18 and 20-years-old appeared in Oamaru District Court today.

Prime Minister John Key and Police Minister Judith Collins have suggested tougher penalties to send a clear message that police should be feared and respected.

Strengthening respect would start by cracking down on verbal abuse from the public, said Police Association president Greg O'Connor.

The three attacks on officers since Friday were the latest in an ongoing trend, he said.

Seven police officers had been shot in the past year, and assaults were one part of abuse happening at all levels, starting with people calling police "F***ing pigs", Mr O'Connor said.

The union would be calling on Police Minister Judith Collins to have the whole justice system - from judges and police officers to the Independent Police Conduct Authority - come together and build a strategy to stop all abuse, Mr O'Connor said.

Just brining in tougher sentences would have little effect, he said.

Meanwhile, Canterbury University criminology professor Greg Newbold said New Zealand police already had a relatively good relationship with the public - much better than in Australia and especially the United States, where gun-toting officers tended to be "belligerent, arrogant and bullying".

Our police were polite and courteous - and respected - in comparison, because without guns they needed the public's co-operation, he said.

But police scandals, including Louis Nicholas's rape and even the Springbok tour, had eroded police's public image, he said.

People who attacked officers deserved a serious sentence - but sentences would not stop them from happening, he said.

"People don't plan to go out and attack a police officer - they do it on the spur of the moment when they're on the piss."

They would not be thinking about consequences, he said. Instead, assaults on officers were done without thinking and could be influenced by media reports.

"Why have we suddenly got a spate of these things? It's probably just bad luck - but there may be a bit of copycat going on, where these people read about it, and do the same in an alcohol-fuelled state."

There was not much that could be done and getting in dangerous situations was part of policing work, he said.

Tougher sentences would not deter criminals who were not thinking, tasers and pepper sprays were unhelpful when outnumbered, guns would deteriorate police's relationship with the public, and there would always be fired up youth who saw police as the enemy, Mr Newbold said.