Sydney recorded its wettest year in 164 years as authorities braced for major floods in Australia's east on Thursday, with more heavy downpours expected to fall over the next three days, Reuters reported.

With almost three months of 2022 still to go, Australia's largest city has recorded 2,200 mm of rain in a year for the first time since records began in 1858.

By Thursday afternoon, Sydney had received about 2,213 mm (87 inches) of rainfall for the year, surpassing the previous record of 2,194 mm set in 1950, official data showed.

More than 58 mm fell over five hours since 9 am local time (2200 GMT, Wednesday), the Bureau of Meteorology's (BoM) live data showed.

More downpours are forecast for the rest of 2022, as Australia's east coast remains in the grip of a rare third straight year of the La Nina weather phenomenon.

"Heading into late spring and summer, we're still in this active La Nina period so we can expect more and more rainfall and that does increase the risk of flooding," BoM forecaster Jonathan How told ABC television.

During the past two years, floods have struck Sydney's suburbs three times, forcing tens of thousands of people to flee their homes.

With a wild weather system expected to dump heavy rains through the weekend across a wide swathe of Australia's east, authorities warned Sydney residents to watch out for flash flooding and stay away from flooded roads.

Many dams and rivers are already at full capacity. The New South Wales state government has committed to raising the height of the wall at Sydney's Warragamba Dam, which supplies 80% of the city's water, to help prevent future floods.