There will be a huge police presence in Sydney on New Year's Eve with officers armed with semi-automatic firearms to help protect more than one million people expected to flock to the harbour to celebrate.

But the increased policing shouldn't dampen the spirit on New Year’s Eve, New South Wales premier Gladys Berejiklian says.

Despite dozens of officers with Colt M4 semi-automatic rifles on guard to protect crowds on New Year's Eve, revellers have been urged to go about their plans as they normally would.

"We ask people to go about their normal business but of course they can expect to see a huge police presence as well," the premier told reporters in Sydney on Thursday.

"Please know we are doing everything we can to keep the community safe at all times."

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Authorities have warned the public to expect an extra police presence and increased safety measures - police will be out in force, some heavily armed, as well as plainclothes surveillance teams scouring the CBD.

Riot squad officers with the military-style semi-automatic rifles will be equipped to launch a tactical armed assault in response to a high-risk situation like a vehicle attack or mass stabbing.

Barriers and concrete bollards will be in place for additional security on the night.

Related Reading Semi-trailers used to block streets surrounding Pitt Street Mall on Boxing Day

Ms Berejiklian insisted she was confident that authorities had the resources and powers they needed to keep the community safe during the festive period as well as every other time of the year.

"As a government, we feel absolutely obligated to make sure that all of our security agencies are keeping the community safe but our strongest message to everyone is please go about your normal business.

“We make sure that all the authorities have the resources they need and the powers they need to keep the community safe at all times.”

Semi-trailers, bollards used to protect Sydney crowds

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The amping up of policing comes days after semi-trailers were used to block key pedestrian areas in Sydney's CBD on Boxing Day.

Concrete bollards and road closures were also put in place as police worked to protect the thousands of shoppers hitting the sales.

The trucks were used as a protective measure to block vehicle access from streets surrounding Pitt Street Mall and the Queen Victoria Building.

Douglas Tomkin from the University of Technology Sydney’s Designing Out Crime Research Centre team helped draft the government document ‘Safe Places – Vehicle Management’.

He said, in the wake of the Flinders Street incident, bollards and other barriers like chicanes are good ways of averting vehicle-borne attacks.

“They're testing these large bollards, they're driving vehicles into them at high speeds to see what happens... there will be tests on many different types of bollards in the very near future,” Mr Tomkin told SBS News.

“The police have to react when something like this happens. I mean, we all want to be protected. So the quick solutions are these temporary bollards.”

NSW authorities are warning of significant road closures on New Year’s Eve throughout Sydney, including the Harbour and Anzac bridges, and have urged the public to use trains and buses rather than cars to travel on the night.

More than 4,500 extra public transport services will be running to and from the city on New Year’s Eve as the city is swamped in revellers celebrating the end of 2017.

Widespread road closures and clearways during #SydNYE - see map for details https://t.co/x3ZDmShx0W pic.twitter.com/R47gn6poq0 — City of Sydney (@cityofsydney) December 27, 2017

Over 1000 extra trains will be running for New Years Eve to get you to and from the city. With road closures in place, trains are the way to go. Top up your Opal card in advance and don't forget to tap on/off as normal. https://t.co/k1LH9as8JS — Trains Info (@TrainsInfo) December 27, 2017

There are a number of free and ticketed areas for firework vantage points around the CBD. Pre-show entertainment begins at 6pm, with family fireworks around 9pm. The Harbour of Light parade follows along Sydney Harbour at 9.15pm and then the midnight fireworks.

Melbourne is also staying prepared; the city had its first practice run of a new emergency loudspeaker system to boom through streets during possible terror-related attacks, after 65 speaker sets were installed at sites including Federation Square, Flinders Street Station and the Bourke Street Mall.