One person is dead, two police officers have been injured and almost 130 flights cancelled after a month’s worth of rain was dumped on Sydney in just two hours.

A series of thunderstorms battered the NSW coast from Newcastle down to Wollongong on Wednesday morning, causing havoc for commuters and emergency services.

The weather bureau warned more rain and hail was likely later in the day, as authorities urged people to think about alternatives for their afternoon commute or school pick-up.

It said it was Sydney’s wettest November day since 1984.

Hail that fell near Tamworth and workers clearing out a blocked drain. Photo: Facebook/ABC

A person was killed in a crash on The Esplanade in Thornleigh, on Sydney’s upper north shore, while a tree fell on two police officers who were trying to help drivers trapped on a flooded road in North Ryde.

A probationary constable suffered a suspected broken leg and was taken to hospital in a serious condition. Her partner suffered a possible concussion and minor injuries.

“Delay your journey or work from home today – we want fewer cars on the road,” NSW Police Assistant Commissioner Michael Corboy said.

We do not want any further tragedies to happen today.”

He also had a warning for drivers.

“We are really worried about people trying to cross flooded streets or flooded streams in this weather. (And) we’ve already seen idiotic driving today,” he said.

“It is extremely dangerous practice, particularly in smaller cars and we’ve seen people get wash away and killed before on many occasions both in NSW and throughout Australia.”

More than 118 millimetres fell at Observatory Hill in Sydney’s CBD in the six hours to 11am on Wednesday – easily eclipsing the November average of 83.8mm.

Mosman recorded 123 millimetres of rain, while Chatswood had 119 millimetres, including 66 millimetres in an hour.

Shoalhaven’s Porters Creek Dam recorded the state’s highest total so far, copping 168 millimetres on Wednesday morning.

A minor flood warning was in place for the Cooks River at Tempe.

#FRNSW firefighters had to negotiate flooded roads while responding to an alarm in Artarmon this morning. Take care if you’re travelling today and don’t enter floodwater. Like the @NSWSES says – if it’s flooded, forget it! pic.twitter.com/F7TWNTmRKz

— Fire and Rescue NSW (@FRNSW) November 27, 2018

A Transport Management Centre spokesman told the ABC that westbound traffic had been stalled by flooding and a landslide on the Great Western Highway.

NSW Police Chief Inspector Phillip Brooks said the rain would make roads slippery and unpredictable.

“We’re asking all road users to perhaps reconsider the need to be on the road through what will be a severe rain event,” he said.

“Drivers, riders, cyclists and pedestrians need to make sure they are safe on our roads.”

Sydney Airport repeatedly closed one of its runways on Wednesday morning as it tried to operate amid strong winds and 45 millimetres of rain.

About 130 domestic flights and four international flights were cancelled due to the weather.

A Qantas spokesperson said the airline was monitoring the situation as the deluge caused travel chaos.

“We’re closely monitoring the weather and thank our customers for their patience as we work to get them on their way as quickly and safely as possible,” the spokesperson said.

“We encourage customers to make sure their contact details are included in their booking in case they need to be contacted about flight changes.”

My gf is currently trying to swim to work…

This is near the Fish Markets in Glebe 😲 #SydneyStorm pic.twitter.com/0fMcGzKhIW

— Edwin Smith (@edwin_smith1) November 27, 2018

The NSW SES had received more than 280 calls for help by 9am as severe thunderstorms swept across the harbour city.

By midday, it had 50 crews responding to 560 calls, having already rescued 12 people from floodwaters.

An SES spokesman said the major concern was people driving into flood waters, putting their lives and the lives of volunteers at risk.

Roseville Bridge and dozens of roads across Sydney were shut due to flash flooding, while a landslide on Spit Road in Mosman also caused issues.

An overflowing weir on the Parramatta River led to ferries being cancelled between Sydney Olympic Park and Parramatta. In the city’s inner-west, rail services were cancelled due to standing water.

By midday, more than 5000 properties were without power across Sydney, including the CBD and northern suburbs, with lightning strikes and strong winds damaging lines.

AusGrid said the torrential downpour flooded an underground substation at Wynyard.

A severe thunderstorm warning for heavy rainfall, damaging winds and large hailstones remained current for the Sydney metro, the Hunter and the Illawarra regions and parts of the Mid North Coast, South Coast, Central Tablelands, Southern Tablelands, North West Slopes and Plains and Northern Tablelands.

The heavy rain isn’t expected to ease until Wednesday night. Damaging winds could hang around until Thursday.

If you are trapped by flash flooding, seek refuge in the highest available place and ring 000 if you need rescue.

For emergency help in floods and storms, ring your local SES Unit on 132 500.

-with AAP