Massive hailstones, lightning and torrential rain have battered Australia's east coast overnight resulting in thousands of power outages and dozens of cancelled flights. Efforts to clear water, branches and debris and restore power to homes in the Greater Sydney area have begun after some suburbs were pummelled with up to 120mm of rain and golf-sized hailstones. Dangerous thunderstorms were detected near Blacktown and Riverstone, the Bureau of Meteorology said on Thursday evening. The storms moved east with severe thunderstorms hitting the city and eastern suburbs by nightfall. Images from the city's west showed giant hailstones pounding cars while almost 20,000 lightning strikes were recorded across the greater Sydney area. Mona Vale in Sydney's northern suburbs received the most rainfall with an astounding 160mm over a 24-hour period. Figures show rainfall across New South Wales varied with reports of 66mm in the western suburbs, 22mm near Liverpool, and 52mm south west in Ingleburn. The downpour triggered flash flooding, power outages and more than 600 calls to the rescue service and about 25,000 homes experienced power outages, according to Nine. Roads, trains and even flights were delayed and diverted away from Sydney's airports. T2 at Sydney Airport reported more than 40 cancellations on Thursday, and 20 more domestic flights were cancelled this morning. So far, two international flights were cancelled on Friday while a small number of flights have been delayed. Meteorologists have warned the wet weather isn't slowing down and could last until early or mid next week. Friday is forecast to bring showers and thunderstorms to the state's east possibly extending to the northwestern slopes. The rain is not expected to be as widespread as Thursday night, but will pick up over the weekend. Showers are forecast on Saturday extending to northern inland areas while on Sunday showers will likely reach the far northern inland with a chance of thunderstorms in the north. Bureau of Meteorology is predicting more hail in NSW and are monitoring the Queensland border for hail as well. The thunderstorms caused chaos on the roads, where incredible dash cam footage captured the dramatic moment a lighting strike hit an electrical pole just metres away from the motorist driving in the Shoalhaven area south of Sydney. The SES received more than 350 calls for assistance regarding fallen trees and damaged roofs. Blacktown, Goulburn, Liverpool and The Hills were among the most affected areas. SES volunteers rescued a person from a vehicle stuck in floodwaters in Wollongong. 'Heavy rain and thunderstorms will affect eastern districts of NSW during the next few days. However, figuring out when and where the heaviest rain will fall is particularly difficult with this system,' Weatherzone tweeted. Further north, Brisbane is also in for a soaking with 30mm of rain forecast for Friday and 15mm for Saturday. Thursday night's storms come three months after a freak summer storm that caused widespread chaos across Sydney was declared an 'insurance catastrophe'. Another storm also caused extensive damage and flash flooding last month.