Heavy rain brought flash flooding to Australia’s largest city, Sydney, on Saturday, prompting rescues and evacuation orders for several low-lying suburbs.

Emergency authorities said they carried out 13 rescues and received 297 calls for assistance from residents in Sydney, the capital of New South Wales state, in the 24 hours to 5 a.m. local time, because of floods sparked by the heavy rain.

Ten emergency evacuation orders were in place for suburbs in the city’s northwest, the New South Wales State Emergency Service (SES) said in a statement on Saturday morning.

The nation’s weather forecaster warned that major flooding could occur in the northwest of Sydney, a city of about 5 million, later on Saturday.

Sydney's Hawkesbury-Nepean valley is a floodplain prone to dangerous flooding, as it is fed by five tributaries and has chokepoints limiting flows to the sea, so water backs up during heavy rain.

SES Acting Assistant Commissioner Dallas Burnes told the Australian Broadcasting Corp. that there was “still a lot of water moving around” and urged affected residents to be prepared to leave their homes.

New South Wales Emergency Services Minister Jihad Dib said the rain had fallen on swollen catchments, resulting in “a much more profound effect”.

“Our dams are full, our waterways are full, our grounds are saturated,” Dib said in a televised news conference in Sydney, adding that some roads and bridges had been affected.

The latest emergency comes after more than 150 people were rescued from floodwaters in eastern Australia in April.

Flooding is the second-deadliest type of natural disaster after heatwaves in Australia, accounting for about 20% of natural disaster deaths between 1900 and 2022, according to the federal government’s Australian Climate Service agency.