The weather wreaked havoc on transport on Wednesday afternoon, with lightning strikes, downed trees and heavy rain causing delays on roads and across the Sydney Trains network.

Volunteers from the State Emergency Service have responded to more than 400 calls for help since bands of storms began to sweep across the city just in time for the evening commute.

The Bureau of Meteorology finally cancelled its thunderstorm warning on Wednesday evening at 9.10 pm for Sydney but an alert remains in place for inland regions. (See chart below).

"The immediate threat of severe thunderstorms has passed, but the situation will continue to be monitored and further warnings will be issued if necessary," it said.

Lightning and strong winds disrupted power to more than 33,000 homes and businesses "at the height of the storm", mostly in Mount Druitt and the Hills District, power company Endeavour Energy said.

The SES was called to 160 reports of storm damage in Mount Druitt, as well as conducting flood rescues. At 9pm on Wednesday, 13,500 homes remained without power and were expected to stay that way overnight.

"The most significant damage has been in the suburbs in and around Plumpton where lightning interrupted all supply from the major substation providing electricity to the area," Endeavour said in a statement.

"This affected power to 14,000 homes and businesses across Whalan, Lethbridge Park, Rooty Hill, Bidwill, Blackett, Shalvey, Dharruk and Emerton."

Trees down

Trees have also brought power lines down across the city, with crews expected to work late into the night making repairs.

A large tree was ripped from the ground in Castle Hill, falling on a fire hydrant and causing it to spray water, as hundreds of lightning strikes hit around Sydney.

Endeavour said the "widespread extent" of damage means some homes will remain without power overnight.

From 9am to 6pm on Wednesday, 42 millimetres of rain fell at Lidcombe, with 46mm at Appin, 44mm at Sydney Olympic Park and 30mm at Baulkham Hills.

As "severe weather conditions" hit the city, commuters were advised to expect delays for their journey home. Sydney Trains cancelled several planned services on the North Shore line and Western Line, from Central to Hornsby and Blacktown, and commuters were told to expect delays with others.

On the Central Coast and Newcastle train line, there were "major delays" due to "urgent signal equipment repairs caused by severe weather conditions".

Ferries between Parramatta and Rydalmere were replaced by buses, as Parramatta Weir overflowed.

Drivers were also advised to take care, as multiple sets of traffic lights were blacked out in western Sydney and a tree fell onto a car at Mulgoa Road in Mulgoa at around 3.15pm.

Paramedics responded, although the person trapped inside was not injured.

Other regions

The storms also lashed the Central Coast, impacting Patonga, Woy Woy, Umina and Kilcare and moving towards the north-east.

Ausgrid said about 2700 homes and businesses were left without power in the region.

Tuesday's storms dumped about 25 millimetres of rain on Observatory Hill, with some regions such as Richmond collecting more than 40 millimetres.

Flights in and out of Sydney Airport were affected by the latest deluge, with the airport advising people to contact their airlines for updates on schedules.

A southerly change arrived late on Wednesday afternoon, providing additional lift for the moist air mass over the region.

The thunderstorms could last well into the evening and potentially extend into the early hours of Thursday, said Rebecca Kamitakahara, a bureau forecaster.

Late on Wednesday, the bureau issued a warning for severe thunderstorms that were "likely to produce heavy rainfall that may lead to flash flooding, large hailstones and damaging wind" over the next few hours

Locations which may be affected include Orange, Tamworth, Gunnedah, Dubbo, Parkes and Wellington.

Good news

The good news, though, is that from Thursday onwards conditions should start to dry off, with only a few showers forecast by the bureau for the coming week.

The bureau has collected at least 0.2 millimetres of rain at Observatory Hill on all but four days so far this month.

The record number of days with some rain in Sydney in March is 26 days, recorded back in 1870.

The arrival of the cool change will lower temperatures a couple of degrees for coming days after Sydney reached 30 degrees for the first time this month.

Despite the lack of particularly hot days of late - unlike Sydney's record hot summer - March is well on course to be yet another warmer-than-average month for the city.

with Georgina Mitchell