Sydney's injecting room will be extended for 4 more yrs

But Health Minister Reba Meagher said the government would be prepared to wind up the Kings Cross centre if demand for its services dropped in the future.

"The bill to be introduced into the NSW Parliament later today will for the first time establish a threshold for client attendance levels," Meagher said.

"If the centre's utilisation falls below 75 per cent of the current daily levels, a formal review will be triggered into the economic viability and need for the centre."

She said the decision to increase the trial comes after a report on the centre by the National Centre in HIV Epidemiology and Clinical Research at the University of NSW.

The report found the the MSIC reduced the impact of overdose related events, instances of public injecting and community visibility of injecting drug use.