Some sharks lurking around New Zealand waters this summer are in more danger than the swimmers they scare, the National Institute of Water and Atmospheric Research (Niwa) says.

The rig shark is a common sight in coastal waters, estuaries and inlets over spring and summer but is also a regular on takeaway shop menus.

"Rig is most often served as the fish in fish 'n' chips. So if there's a shark beside you in the sea, it's probably in more danger than you are," Niwa fisheries principal scientist Malcolm Francis said.

"Rig are a social fish... so you could find yourself surrounded by a group of friendly sharks, so friendly that if you put your hand in their mouth they don't bite back."

Dr Francis' comments follow a series of shark sightings around New Zealand and subsequent warnings to steer clear of the water.

Wellington maritime police yesterday cleared a popular bathing spot after a 2-1/2m hammerhead shark was spotted in the harbour.

Dr Francis said rig sharks -- also known as lemon fish, spotted dogfish and smooth-hound - grow to about 1.5m and have small, distinctive white spots.

They feed mainly on creatures that burrow into the sea floor, especially crabs, he said.

Rig sharks live near the sea floor and are often caught in bottom set and trawl nets.