A storm system battering Australia's east coast is expected to topple records, with Sydney set to smash the mark for its wettest-ever year by this weekend.

The Daily Mail Australia reported Sydney copped a bucketing on Thursday morning with 27.6mm of rain already reported as of 8am AEDT.

Meanwhile, showers will increase in Melbourne throughout the day and Brisbane will also cop some light rain.

The website said the downpour was expected to continue in Sydney through to Monday, while falls would ease into occasional showers in Victoria with rain coming and going in southern Queensland. 

This week's rain is expected to break the all-time record of 2,194mm set in 1950.

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