Parts of Sydney's eastern suburbs were thrown into chaos on Thursday after an underground cable fault cut power to 45,000 customers in the area.

Homes and businesses in suburbs including Double Bay, Edgecliff and Bondi Junction lost power at 11.26am, forcing shops to close, disrupting council services and leaving hospitals relying on backup generators for essential services.

By 12.20pm power was restored to 10,000 customers around the Double Bay area, and an Ausgrid spokeswoman said crews restored power to the remaining 35,000 by 12.37pm.

The blackout was felt widely, affecting the Sydney Children's Hospital and Prince of Wales Hospital in Randwick.