The shark alarm went off at about 12.30pm on Sunday, closing the beach for an hour.

Hunter Surf Life Saving duty officer Luke Wiseman said swimmers were removed from the water until 1.30pm for additional surveillance, including a surf lifesaving drone and jet skis.

Volunteer lifesavers and council lifeguards were particularly alert to the presence of sharks at the weekend, given recent activity.

Hunter Surf Life Saving drone operator Brad Fox said they were "absolutely vigilant".

Mr Fox said a shark was also spotted at Newcastle beach on Saturday.

"The standard is the council lifeguards close the beach for an hour when they get a marine species sighting of concern. They then do a reassessment," Mr Fox said.

Surf lifesavers reported the shark as three to four metres long and "bigger than the rescue board it was spotted from".

Newcastle and Nobbys beaches were subsequently closed for an hour.

While the shark wasn't spotted at Nobbys, it was closed on Saturday "as a precaution".

Mr Fox added that Nobbys was part of the statewide SharkSmart program in which UAVs [unmanned aerial vehicles] - also known as drones - were used for spotting sharks.

Mr Wiseman said there were high numbers of people at Hunter beaches on Sunday due to the good weather. As well as the shark sightings, there was a medical incident at Caves Beach.

"Volunteer lifesavers worked well with Newcastle and Lake Macquarie council lifeguards," he said.

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