Four rescued as thunderstorms soak NSW

Four people have been rescued from rising floodwaters in Sydney's west as severe thunderstorms soaked NSW for the second day in a row.

The State Emergency Service says it responded to 500 calls for help on Tuesday, including three from people stuck in vehicles and one from a house in Luddenham, near Penrith.

About 90 children were also evacuated from a childcare centre in Orchard Hills as the torrential rain swamped streets around the facility.

"Parents weren't able to reach the centre so our crews used some high clearance vehicles to move the children and get them home," SES spokesman Phil Campbell told AAP.

Most of Tuesday's call-outs were for leaking roofs and flash flooding in western Sydney and on the state's Central Coast, he said.

Erskine Park received more than 60mm of rain since 9am, while Seven Hills Blacktown and Baulkham Hills all recorded more than 50mm.

The state's public transport system also took a hit from the wild weather with buses replacing trains between Mount Victoria and Lithgow on the Blue Mountains Line due to damaged equipment from lightning strikes.

The Bureau of Meteorology (BoM) predicts the rain will continue in the Sydney region and eastern parts of the state on Wednesday but said the immediate threat of severe thunderstorms had eased.

A coastal trough will deepen off the north coast on Wednesday and persist into the weekend, with the potential for heavy rainfalls to build up in the northeast by the end of the week, according to BoM.

A flood watch is also in place for river valleys in the state's northeast, including Brunswick, Wilsons, Orara and Bellinger.