Wild weather: Two storms approach Sydney on Sunday night. Photo: Wolter Peeters
The roof of the Blue Mountains Hospital partially collapsed on Sunday night as wild weather including hail stones, flash flooding and blackouts spread across Sydney.
Ten patients were relocated while the area was assessed by engineers.
Superintendent Paul Johnstone, Manager of Operational Staffing at Fire and Rescue NSW, said 20 firefighters were working alongside police, ambulance and SES in Katoomba to clear flooding and stop further water coming into the hospital.
A spokesperson for the Blue Mountains hospital said crews were investigating the extent of the collapse.
"They have had some damage, they're assessing the damage at the moment, the general manager is down there right now," the spokesperson said.
She confirmed no patients had been injured.
"All the damage is in the non-clinical areas, so they're non-patient areas. "All patient bedrooms are dry and safe."
Fire crews responded to 50 calls as a damaging storm cell made its way from Wollongong up the coast.
"We've had flooding, wires down, we had trees collapsed onto high-voltage power lines at Whalan," Supt Johnstone said.
"We've also had a roof collapse at Katoomba sports and aquatic centre, which has been badly damaged by flooding. There were no occupants, and one fire engine is on-scene to remove water and prevent further damage to the building."
Peter Payne from Endeavour Energy said crews were working to return power to thousands of customers affected by the storms.
"We had about four-and-a-half-thousand customers out between Plumpton, Whalan and St Marys," Mr Payne said.
"We had a slow-moving thunderstorm hit western Sydney that lasted about an hour, and that brought lots of lightning and torrential rain. Lightning has hit the power lines and interrupted power."
The Bureau of Meteorology issued a severe thunderstorm warning for Sydney, the Blue Mountains, the Hawkesbury and central coast, advising people to prepare for large hailstones and heavy rainfall.
The cell was "extremely quickly moving", rumbling across the greater Sydney area at between 60 and 80 km/h, a bureau spokesman said.
"Severe thunderstorms were detected on the weather radar near Parramatta, Katoomba and Richmond. These thunderstorms are moving towards the north," said the bureau's warning issued at 8.20pm (AEDT).
No storms are expected around Sydney on Monday but the bureau is predicting light showers.