The NSW energy minister Matt Kean has urged residents across the state to reduce electricity usage as the Berejiklian government scrambles to determine the extent of fire damage to the Snowy Hydro's transmission lines.

The NSW grid's links to Victoria went down late on Saturday afternoon, with Mr Kean issuing a statement urging all residents to preserve power.

"The extensive bushfire activity in the Snowy Mountains and other areas of the state have had an impact on our electricity supplies,” Mr Kean said.

Just before 7pm, 14,000 people had lost power in Sydney's north and south-west, and Port Stephens. Greenacre, Campsie, Punchbowl, Hornsby, Chatswood and St Ives were affected, as well as Port Stephens on the Central Coast.