Heavy rains along Australia's east coast over the weekend have caused the worst flooding in half a century in some areas.

The flooding has forced thousands to evacuate and damaged hundreds of houses, according to local officials.

“Yesterday we were hoping it will only be a one-in-20-year event, now it looks like a one-in-50-year event, and potentially another 4,000 people may be asked to evacuate in and around that Hawkesbury region and parts of western Sydney,” New South Wales Premier Gladys Berejiklian said at a televised briefing.

Heavy rains on Saturday sparked dangerous flash flooding, which unmoored houses, engulfed roads, broke trees, and damaged road infrastructure in the state. (ILKHA)