TORONTO -- About 900 hydro workers are trying to restore power to thousands of Ontarians still in the dark after a destructive thunderstorm.

Hydro One spokeswoman Alicia Sayers says the utility has called in all of its staff to work on reconnecting about 20,000 customers.

Nearly 50,000 had their power knocked out yesterday when a severe weather system blew through southwest and southern Ontario.

Hydro One estimates the power will be back on for most of its customers by about 10 p.m. tonight.

Police say the heavy rain, hail and high winds brought on reports of downed trees and power lines along with minor injuries.