The bad weather composed of heavy rain, strong winds and high tides hitting Australia's state of NSW is expected to get worse through Tuesday until Wednesday.

Since Monday, the region has received more than 100 millimetres of rain fall, forcing authorities to close roads.

"There's a likelihood of another 50 millimetres or so in the next few hours," State Emergency Service spokesman Kevin Anderson said in anticipation of the heavy rains on Tuesday.

The following roads have been closed due to flooding and water on roadways:

• Bullamalita Road
• Painters Lane
• Coopers Lane
• Mills Road
• Bulls Pit Road
• Range Road
• May Street
• Carrick Road
• Chinamans Lane
• Towrang Road
• Currawang Road
• Mayfield Road
• Sandy Point Road
• Muffets Road
• Lumley Road, towards Oallen Ford Road
• Windellama Road, past Mountain Ash Road and near the airport
• Highlands Way at Barbers Creek
• Jaqua Road crossing
• Blackshaw Road underpass
• Lansdowne Bridge
• Oallen Ford Road Bridge over the Shoalhaven River

Also closed were Gurrundah Road and Nerriga Road.

NSW Police likewise said the Windellama and Range Roads may also be closed in the coming hours.

Flooding and water on roadways have also forced the closure of the railway underpass, Landsdowne Bridge, May Street Bridge, Muffets Road and Lumley Road, the Goulburn Post reported. Towrang Bridge may be cut off by midday.

Australia's Bureau of Meteorology said the Illawarra region had experienced about 150-200 millimetres of rainfall on Monday, which is double its monthly average rainfall in 36 hours.

On Tuesday, the region could expect wind gusts of up to 80kmh, according to the bureau.

About 50 millimetres of rain is expected to fall across Sydney before the wet weather eases on Thursday.