Windscreen washers at Christchurch intersections could be fined up to $20,000 after violent incidents prompted police to crack down on the practice.

Sergeant Greg Hume said motorists had made a "large number" of complaints about young windscreen washers damaging their vehicles or intimidating them in the last year.

Hume recalled a businessman was attacked by two or three windscreen washers at the Moorhouse Ave/Barbadoes St intersection about a month ago, after the man confronted a washer who had smashed his car's side window.

Thefts of squeegees from petrol stations was an ongoing issue.

In May, a petrol station manager said 20 squeegees had been stolen from his premises over four weeks.

Hume said the thefts showed a lack of empathy on part of offenders, as it affected petrol stations' ability to offer quality customer service.

A 16-year old had been referred to Police Youth Services for stealing two squeegees from the same service station twice, he said.

Since Monday, police have informed windscreen washers they faced fines of up to $20,000 under the Christchurch City Council's public places bylaw if they worked without a council-issued commercial licence.

Windscreen washers have been an increasing nuisance at the Linwood Ave/Buckleys Rd, Moorhouse Ave/Barbadoes St, Moorhouse Ave/Madras St, Avonside Dr/Stanmore Rd and Aldwins/Ferry roads intersections.

Hume said he had "no doubt" youth gangs were the main culprits, and expressed concern turf wars over intersections could develop if the practice continued.

He encouraged motorists to report windscreen washers to the police.

Hume said police had been recording washers' details during the "warning phase", which would continue for about a month to give the washers an opportunity to avoid prosecution.

However, teens aged 14-16 had received court summons for returning to their squeegees hours after being warned to relinquish them, Hume said.

Council policy team leader Claire Bryant said both council and police had sought legal advice on how to thwart windscreen washers after complaints began escalating about a year ago.

Both Hume and Bryant said the apparent profitability had sparked increased numbers to give it a try.

Bryant said the council would continue to support police in their efforts to curb the practice, which posed a health and safety risk to washers, and a nuisance to motorists by disrupting vehicle flow.

Last year, Auckland police and council compliance officers began a crack-down on windscreen washers at the intersection of Great South Rd and Cavendish Drive, confiscating squeegees and fining offenders under Auckland Council's public safety and nuisance bylaw.

Last month, Auckland Council gave Counties Manukau police authority to trespass people at the intersection of Bairds and East Tamaki roads in Otara, after receiving almost 100 complaints about windscreen washers at the intersection in the past year.

Sergeant Jonathan Milne said "Operation Wash Up" had resulted in a drastic decrease in windscreen washing at the intersection over the past month.

The operation would be extended to other areas of Counties Manukau.

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