NSW residents need to adjust to seeing elite police officers carrying semi-automatic rifles as dozens of the weapons are rolled out in time for the festive period, Commissioner Mick Fuller says.

Mr Fuller on Monday announced about 50 riot squad officers had completed a 10-day intensive training course and would carry the weapons.

The move was flagged in June, and by the middle of next year the entire riot squad - about 100 officers - will be armed with the high-powered weapons.

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"We have to get used to it," Mr Fuller told reporters in Sydney on Monday.

"There's no point in us pretending the environment hasn't changed - the organised crime environment, the terrorism environment."

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The heavily-armed officers will be deployed in active armed offender situations, such as terror incidents.

But Deputy Commissioner Dave Hudson said the commissioner could also approve their deployment to large gatherings, including New Year's Eve events, because of their deterrent effect.

"That will be an assessment made on a case-by-case basis," he said.

Mr Hudson said most overseas incidents occurred at distances over 25 metres, sometimes up to 100 metres, and the current Glock weapons weren't as effective at that distance.

He also cited a change in the environment "over the last several months" to justify the upgrades.

"We need to think differently, we need to deploy differently."

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The increase in firepower comes after police in Victoria thwarted an alleged plot to use an automatic rifle to shoot as many people in Federation Square on New Year's Eve.

Mr Fuller said a change in the national terror threat level, which has remained at "probable" since 2014, could mean the specialist officers would be deployed more often.

"I'm not a sensationalist either and we're not going to have police patrolling with long-arms," he said.

"But if something happened tomorrow, I want people to know that we're ready to go, we've got the capability ready to go."