Commuters heading into and out of Sydney Airport should expect significant delays, with more than 100 domestic flights cancelled due to bad weather.

Key points: Campbelltown and Wollondilly were the worst-affected areas

Campbelltown and Wollondilly were the worst-affected areas The SES responded to more than 400 calls for assistance

The SES responded to more than 400 calls for assistance Winds of up to 107 kph were recorded at Coonamble Airport

Sydney Airport said 62 arrivals and 65 departures had been cancelled, as a result of severe thunderstorms that swept the city this afternoon.

International flights were less affected, with no cancellations, however travellers should expect delays.

As the storm moved through, Woy Woy and Umina were the hardest-hit areas, with heavy rain and lightning.

Ausgrid said up to 28,000 properties lost power on the Central Coast, and it was working to restore it as quickly as possible.

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Visibility on the M1 Pacific Motorway was very low as the storms swept through shortly after 3:00pm.

Trains between Hornsby and Gosford were cancelled for some time due to the power supply issues, the Transport Management Centre said.

Trains are now running again but buses are still replacing some trains, so commuters should allow plenty of time, a spokesperson said.

The Bureau of Meteorology (BOM) had warned NSW to "be prepared to batten down the hatches", forecasting more wild weather after a night of thunderstorms.

Avon Fire Tower to the south-west of Sydney recorded 86mm, while 48mm was recorded at Dungog in the Hunter and 44mm at Putty Tea Rooms, also in the Hunter.

Kemps Creek recorded Sydney's heaviest rainfall, with 43mm falling since 9am.

Richmond and Campbelltown recorded 27mm of rainfall while 23mm fell in Terrey Hills.

BOM's Rob Taggert warned that residents on the coast, the ranges and the north-west slopes should expect short bursts of very heavy rainfall that could result in flash flooding.

He also warned of damaging wind gusts and large hail, with stormy conditions expected to last into the weekend.

Around 1:40pm, BOM said they detected "very dangerous thunderstorms" set to impact parts of Newcastle, including Raymond Terrace and Newcastle City.

They also forecast "giant hailstones, heavy rainfall and damaging winds" for parts of the Maitland/Cessnock and Greater Newcastle region.

Storms continued through the night

The forecast follows the SES report that it had received more than 400 requests for assistance since the storms hit on Thursday afternoon.

Emergency services carried out at least seven flood rescues, with at least four in Menai, Fairfield, Auburn and Guildford after people became trapped by flash flooding.

Phil Schafer from the SES said the worst affected areas were Albury, Wagga Wagga, Orange and Wollondilly, saying the jobs they attended were "quite widespread".

Thunderstorms caused power outages and stopped rail lines in Sydney, last night. ( Instagram: Alex Savidis )

Power outages caused significant commuter chaos throughout the Greater Sydney area.

A power outage also caused trains on the Blue Mountains line, between Katoomba and Springwood, to stop running for some time.

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The Transport Management Centre said weather conditions at Wentworth Falls were to blame.

Outages at Wests League Club in Campbelltown also caused poker machines to lose power, but most of the machines were back on by 9:30pm.

BOM said 41mm of rain fell between 7:35pm and 8:05pm at Auburn in Sydney's west, while 37mm fell at Guilford during the same time.

Bowra Sugarloaf in the state's mid north coast received the most rain, with 79mm.

Wind gusts of up to 105 kilometres per hour were recorded at Narrabri West on the north-west slopes, and 107kph at Coonamble Airport.

BOM earlier issued a severe thunderstorm warning for the eastern half of the state, stretching from Tenterfield and Moree in the north, through to Newcastle, Gosford and Sydney and south to Albury and Deniliquin.

It said by 9:00pm, the severe thunderstorm threat had passed.

NSW SES duty operations coordinator Emma Delaney said most of the calls they had received were from the Sydney metropolitan area and involved damage to roofs, trees down and water entering homes.