Police have praised the behaviour of Sydney New Year's Eve revellers, with only a small number of people arrested as celebrations took place across the city.

On one of the busiest days of the year, 38 people were arrested, including nine in the CBD.

NSW Police called it a "great success".

"People did come in, they listened to directions of police, they listened to event management, and I think by and large people had a great time," Assistant Commissioner Peter McKenna said.

"We saw people come together after a heartbreaking month."

More than nine tonnes of fireworks were used. (ABC News: Abubakr Sajid)

At Guildford, in the city's west, four people were arrested for allegedly throwing fireworks that injured two children and a man.

Two girls, aged 12 and 14, were taken to hospital with non-life-threatening injuries.

A record 2,500 police officers were on patrol overnight, with some bearing long-arm guns in the wake of the Bondi terror attack.

Police said it was to provide a sense of security for crowds and not because of an increased threat.

'We couldn't have wished for more'

Some revellers camped out along the harbour at 4am in the morning to secure the best vantage point.

More than a million people attended the Sydney Harbour fireworks and more than half a billion watched the 12-minute, colourful display around the world.

Organisers said nine tonnes of fireworks were used and more than 40,000 pyrotechnics.

More than 40,000 pyrotechnics were used in the display. (ABC News: Abubakr Sajid)

More than a million revellers attended the Sydney Harbour New Year's Eve event. (ABC News: Abubakr Sajid)

It was a night of celebration and emotion. (ABC News: Abubakr Sajid)

City of Sydney Lord Mayor Clover Moore said she thought attendee numbers "were slightly down", but a million people still gathered for the "magical" night.