People sit on Nobbys Beach on Tuesday after it was closed. Photo: Darren Pateman

Newcastle's beaches are closed on Wednesday for a record fifth day in a row after four shark sightings in 24 hours, a police boat's close encounter and the discovery of the washed-up remains of a dolphin suspected to have been killed by a shark.

Nobbys Beach inspector Scott Hammerton was on a jet-ski investigating a shark lingering at the end of the breakwall about 2.30pm on Tuesday when water police called him to the northern end of Burwood Beach.

This dolphin was possibly attacked by a shark. Photo: Craig Hollier

"A four-metre great white came up to the police launch, had a look at the boat, flicked its tail and went underneath it," Mr Hammerton told The Newcastle Herald.

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"It was right on the surface, about 50 metres behind the waves, before heading into the surf zone.

"At this point, we decided to call it off, it was not worth getting any closer."

Surfers ride the waves at Merewether despite shark warnings. Photo: Darren Pateman

Mr Hammerton said the sightings confirmed at least two sharks were cruising along the city's coastline.

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Newcastle beaches closed for record fifth day after four shark sightings in 24 hours