An elite NSW Police squad has been issued with semi-automatic military assault rifles as part of a plan to protect New Year's Eve crowds from the threat of terrorism.

Forty-seven officers from the Public Order and Riot Squad (PORS) have been equipped with high-powered Colt M4 Carbine rifles, similar to those used by elite armed response units overseas.

The high-powered weapons will allow PORS officers to launch a tactical armed assault in response to a high risk situation like a vehicle attack or mass stabbing.

NSW Police Commissioner Mick Fuller said the officers would not carry the guns while on a standard patrol but said the weapons would be stowed in squad cars where they would be close at hand if needed.

"If there was a change in the national terrorist threat level then I could put long arms on the street today," Commissioner Fuller said.

"If there was a specific threat somewhere they would be deployed, either in a preventative way or a disruptive way, so we certainly won't hesitate in using them.

"But what's important is that if there is a change to that threat that we have the ability to have officers on the street with those firearms … we don't have to wait for that capability now."

NSW Police Force are introducing high-powered guns to bolster Sydney's weaponry in the holiday season. ( ABC News: Jessica Kidd )

The terrorism threat level has remained at "probable" in Australia since September 2014.

NSW Police Minister Troy Grant said he hoped the firearms would "never have to be used".

"The community will be comforted by the fact the police have this capability to keep them safe," he said.

He said the guns would be available to protect Sydneysiders across the Christmas period and New Year's Eve, where hundreds of thousands of people are expected to cram into harbourside areas to celebrate.

The remaining 50-odd PORS officers will be trained and issued with the Colt M4 Carbine by mid-2018.