More than 10,000 households and businesses left without power due to intense thunderstorms.

The four victims, including a 36-year-old couple and a 19-year-old man, were sheltering under a tree near the famous landmark during a violent storm on Monday when they were struck, ambulance workers said.

The New South Wales ambulance service’s Dominic Wong told reporters that the victims suffered burns and presented with cardiac symptoms after the incident at Sydney’s Botanic Gardens.

“They all had a brief loss of consciousness,” Wong said. “If you’re boating, you should get ashore and seek shelter, and you should not be seeking shelter under a tree.”

The four, two men and two women, were taken to hospital after being treated at the scene by paramedics and are in a “serious and stable” condition, according to authorities.

Sydney was battered by intense thunderstorms on Monday that left more than 10,000 households and businesses without power and caused serious delays to air passengers and road and rail commuters.

About 75,000 lightning strikes were detected within 100km (62 miles) of Australia’s largest city between 11am and 2pm, according to Weatherzone’s Total Lightning Network.

Sydney airport’s main runway was closed for about 20 minutes earlier in the day after a lightning strike tore a hole in the tarmac, resulting in the cancellation of more than 30 departures and delays to about 340 services.