The giant fish has been spotted regularly off the beaches of Newcastle, in New South Wales, over the past week and it is believed to be around 5m (16ft) in length and to weigh in at around 1700kg (3748lb).

The bodies of several dolphins have been washed ashore with huge bites taken out of them. Further sightings in the area indicate that in total there may currently be at least two – and possibly three – large sharks patrolling Merewether and Burwood beaches. Onlookers also saw a shark attack a dolphin at the northern end of Nobbys Beach.

Lifeguards say the biggest shark is “of a size that has not been seen before around Newcastle”. Beach inspector Scott Hammerton described his encounter with the giant predator to the Newcastle Herald.

“A four-metre great white came up to the police launch, had a look at the boat, flicked its tail and went underneath it,” he said. “It was right on the surface, about 50m 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.”

The authorities are reluctant to reopen the beaches until at 24 hours pass without a shark sighting.

Sydney’s famous Bondi Beach was temporarily closed after shark sightings earlier this month. However, it is Western Australia which has borne the main brunt of great white attacks, with eight fatalities in the last five years. The most recent death took place in December, when 17-year-old Jay Muscat was attacked by a great white while spearfishing off Cheynes Beach.