Police have warned that lives will be at risk if Parliament does not pass urgent police surveillance legislation.
Parliament's Justice and Electoral committee on Wednesday heard submissions on the Video Camera Surveillance (Temporary Measures) Bill, which will clear the way for the police to resume the use of hidden cameras.
The bill is the Government's response to a Supreme Court ruling that deemed the use of hidden cameras illegal.
Police Commissioner Peter Marshall told the committee that police are losing crucial evidence every minute their secret cameras are turned off.
Mr Marshall said 13 covert surveillance police cases are on hold as a result of the Supreme Court ruling, all of which involve serious offending, and there is a real risk of physical harm to the public.
He said in one of those investigations an entire community is at risk of harm from a very serious offence.
Earlier, the Law Commission questioned the scope and retrospective nature of the Government's police surveillance bill.
Law Commissioner John Burrows told the committee it is one thing to give the police new powers for the future but it is another matter to make illegal actions of the past lawful.
And he says it is not just the police that will get wider powers under the Bill but also any agency that can get a warrant, such as customs and fisheries.
"I think the real question is do we really want powers as wide as that in the hands of agencies outside the police."
The committee heard the points of view of the Law Society and the Criminal Bar Society.
The Law Society says the bill effectively amends the Bill of Rights retrospectively.
A spokesperson for the Society, Grant Illingworth, told the committee it will also allow the police to avoid the rules for obtaining an interception warrant to record audio, as they will legally be allowed to use video cameras with microphones, with a simple search warrant.
The Criminal Bar Association warned there would be no proper court scrutiny of police use of covert video surveillance under the urgent legislation.
Robert Lithgow told MPs the bill is very blunt and wants to magically make the unlawful lawful.
He says requiring the police to have a search warrant gives the facade of judicial oversight but is no real protection.
Mr Lithgow also questioned the Government's claim that dozens of court cases and police investigations will be put at risk unless Parliament passes urgent legislation.
"We simply don't accept that there is a fixed number of cases of a significant number which will break down because their investigation process is wholly dependent on covert surveillance."