Democratic Alliance leader Helen Zille on Friday accused Police Minister Nathi Mthethwa of breaching his constitutional duty to prevent crime by taking 50 000 police officers off the street to attend a morale boosting event.

She said that the number represents nearly one-third of the police force. They would be attending a national police day gathering in Bloemfontein on Friday that had raised considerable controversy, mainly because of its estimated cost of R70-million.

"If taking 50 000 police officers off the street is not an interruption to an essential service, then I don't know what is," Zille wrote in her weekly newsletter.

"If a crime that could have been prevented in normal circumstances happens today or tonight, the minister could be found to have been in derelict of his constitutional duty."

She said that this duty consisted of preventing, combating and investigating crime, maintaining public order and enforcing the law to protect citizens' right to freedom and security.

Zille said that there was a legal precedent for suing the police for neglecting their duty in the case of Alix Carmichele who won damages from the ministry after she was attacked by a man released on bail despite a record of rape convictions.

"So, if someone was raped or assaulted today as a result of the decision to deplete our police force for a morale-boosting exercise, there may well be a case against the minister.

"I'm not inciting people to sue the national minister. But government representatives need to understand that, just as they expect citizens to take responsibility for their actions, they must do so too."

Zille added that Mthethwa would do far more to boost police morale, and that of civilians, by working closely with the Justice Department to "overhaul the criminal justice system to effectively catch, prosecute and convict criminals".