More than 4000 customers were hit by outages during and in the wake of the intense weather that struck on Sunday night, Essential Energy said.

Trees and powerlines were felled by strong winds and heavy rains right across the region, the company said on Monday morning.

Gundagai State Emergency Service (SES) members were called out to reports of multiple trees down on the Hume Highway's northbound lanes, near the Snowy Mountains Highway turn-off, after the severe storms passed through, the organisation advised its community on Sunday night.

"Storms moved across southern NSW last night, bringing down trees and causing damage to power infrastructure from Hay and Ivanhoe in the west through to Griffith, Leeton, Wagga and as far north as Young," a spokesperson for Essential Energy said.

"Essential Energy crews have started patrolling powerlines, with extra teams to support local crews with repairs where required."

The Bureau of Meteorology upgraded a severe weather warning for the region to include damaging wind gusts, large hailstones and heavy rainfall on Sunday evening. As of 7.30am on Monday, a total of 4036 customers were without power.

They include 440 in the Wagga and surrounding area, particularly in Forest Hill, Maxwell, Big Springs, Oura Road, East Street and Ladysmith.

The bureau recorded 54.6mm of rain at the Wagga airport and 30mm at the Kapooka staton to 8am on Monday. Griffith received 18.2mm and Yanco 12mm.

More than 1200 Leeton customers have been left in the dark thanks to widespread damage to the electricity network there, Essential Energy said.

That impact is being felt at Yanco, Grong Grong, Midgeon, Morundah, Coleambally, Berembed, Jennings West, Darlington Point, Whitton and surrounds.

Essential Energy teams have started patrols around Griffith, Hanwood and Merriwagga, where more than 1000 premises have lost power, while 770 more in the Hillston and Ivanhoe region are in a similar situation.

"Crews are currently patrolling powerlines across the area, including the main line that feeds power from Hillston to Ivanhoe," the spokesperson said.

"A team is also en route to Ivanhoe to assess damage to consider options for restoring power."

Almost 700 of the company's customers around Young and Maimuru have been hit, with Essential Energy teams returning on Monday morning to continue repairs.

Coolamon and Lockhart are also affected, with 120 in the former and 34 in the latter without power.