All eyes will be on Newscastle's coastline on Tuesday after the sighting of a great white shark closed beaches for a third day.

Lifeguards spotted the large shark on Monday morning and are monitoring its progress between Nobbys and Stockton beaches.

It's believed to be the same shark that was first seen on Saturday afternoon at Merewether Beach and appears to have moved up north, with the entire coastline being shut down.

A Westpac helicopter patrol on Monday morning returned with no sightings but lifeguards will continue their watch today.

Increased marine activity and overcast and warm weather are thought to be possible reasons for the shark's prolonged presence.

© AAP 2015