Asbestos found on Sydney Harbour Bridge

A surprise cache of asbestos has been found on Sydney's iconic Harbour Bridge during road works.

While workers were removing the northern toll booth they uncovered a small amount of asbestos under concrete road slabs thought to be installed in the 1950s, Roads Minister Duncan Gay said.

A qualified hygienist tested the asbestos and said it had low potential for airborne exposure, Mr Gay said.

Authorities will be checking where excess material removed from the site went and how it was disposed of as part of an investigation into the incident.