The roof of a hospital has partially collapsed in the Blue Mountains, after wild weather lashed Sydney's western fringe.
The weather bureau says a severe thunderstorm is producing large hailstones and heavy rain that could lead to flash flooding in parts of the metropolitan, central tablelands and Hunter forecast districts.
Fire and Rescue superintendent Paul Johnston says emergency services are working with engineers at the hospital in Katoomba.
"To help clean up the area, remove water, stop more water getting in," he said.
"In the hospital there's been no evacuations... but 10 patients have been relocated within the hospital."
The State Emergency Service says it is receiving a high volume of calls and is asking residents to be patient, or to call triple-0 in an emergency.
© ABC 2014
11:23 EDT Rising humidity across New South Wales will accompany heating during the coming week, contributing to widespread rainfall and keeping fire danger down.