The heritage-listed Warragamba Dam, located about 70km from central Sydney, started spilling mid-afternoon on Saturday, as rain continues to batter parts of NSW.

The volume of water is expected to increase into Sunday as rainfall and flooding continues, Water NSW said.

Premier Gladys Berejiklian said on Saturday afternoon she had been briefed on the dam situation “in relation to a potential for a one-in-five-year, one-in-10-year, or one-in-20-year event”.

“All three scenarios being planned for,” she said.

She warned residents in the catchment area, as well as those in the mid-north coast, the Hunter, central coast and metropolitan Sydney to be on high alert and ready to evacuate.

Other dams such as Nepean, Cataract, Cordeaux and Avon are also expected to reach capacity and begin spilling on Saturday afternoon, Water NSW said.

If you need assistance due to flooding, call the SES on 132 500.