A female police officer was knocked unconscious in south Auckland last night, while police were trying to contain disorder following the Tonga v Lebanon Rugby League World Cup semifinal game, played in Christchurch yesterday.

The female officer was taken to hospital with a head and arm injury after the serious assault by an unknown man from behind.

Inspector Rod Honan said police are investigating the incident and wish to speak to anyone who has information which may help with inquiries.

"Someone knows exactly who committed this cowardly act and we urge the offender, or anyone with information, to come forward," he says.

"We know a number of people would have seen the offender."

Honan said police staff work tirelessly every day to keep the community safe and violent acts against officers are unacceptable.

"The officer has been discharged from hospital today and will continue to receive support while she recovers at home," he said.

A total of 11 arrests were made in Otahuhu last night; 10 for disorderly behaviour and one for possession of an offensive weapon.

Information should be shared with Counties Manukau Crime Squad on 09 261 1321 or Crimestoppers anonymously on 0800 555 111.