As mass clean-up efforts continue across Sydney, residents across the state are being warned to prepare for more large hailstones, heavy rainfall and damaging winds.

A severe thunderstorm warning has been issued for parts of Northern Rivers, Mid North Coast and Northern Tablelands Forecast Districts.

“Heavy rainfall that may lead to flash flooding and damaging winds in the warning area over the next several hours. Locations which may be affected include Grafton, Tenterfield, Casino, Kyogle, Tabulam and Dorrigo,” explained the Bureau of Meteorology.

Homes along the NSW eastern coast and greater Sydney region were pummelled overnight by severe storms that swept over the region. (Supplied)

The State Emergency Service is advising people to move cars under cover and is warning people to stay away from flood waters.

Mass clean-up efforts have begun across Sydney this morning after the city, and large parts of Australia’s eastern coastline, was pummelled with severe thunderstorms that caused golf ball-sized hailstones, heavy rain and strong winds.

In NSW, the State Emergency Service responded to more than 620 calls for help overnight as the intense weather system swept over the greater Sydney region, as well as the south coast.

At one point, up to 25,000 homes were also without power in the thunderstorms.

Throughout the storm, more than 20,000 lightning strikes were recorded across the greater Sydney area.

Blacktown, in Sydney’s western suburbs, was the worst-hit location. Residents made more than 191 calls for help to the SES, while another 65 were made on the Northern Beaches.

Across the city, 60mm of rain fell in the west, 30mm in the eastern suburbs and 10mm in the CBD after the storm cell rolled up from the state’s south coast and headed towards the state’s central coast.

This morning, clean-up efforts began in an attempt to clear water, fallen trees and branches, power lines and debris from roads around the city.

The NSW SES has renewed yesterday’s warnings to residents to prepare for more stormy weather predicted to sweep over much of the state later today.

(Facebook/NSW SES)

Meanwhile, at Dee Why Beach and Lagoon in Sydney's north the damage from wild and gusty winds produced in yesterday's storms was revealed this morning.

Surfers who visited the popular beach today were confronted with large chunks taken out of the sand after the winds had chopped up parts of the lagoon's edges.

The wild weather also caused chaos at Sydney Airport where passengers were left frustrated as flights were delayed due to the heavy rain and lightning.

The airport was forced to push its typical 11pm flight curfew date in order to deal with the number of disrupted flights.

Surfers at Sydney's Dee Why Beach this morning were confronted with the significant damage the storms did to the popular spot. (9news)

Large chunks of sand were seen taken out of the beach, after the gusty winds had whipped up parts of Dee Why Lagoon. (9news)

In total, at least 60 flights were cancelled overnight and delays ranged in time up to around 90 minutes.

Queues are Sydney Airport this morning appeared sluggish as flight staff worked to clear the backlog of passengers affected by the cancellations, some of whom were left with nowhere to stay after their travels were disrupted.

Forecasters are now expecting more intense weather to hit NSW again today, with more rain showers and thunderstorms predicted along the coast up to the Northern Tablelands.

Heavy rainfall could again fall over the central coast today and strong winds should see temperatures stay around the mid-20s.

"As a total, (we received) about 630 calls for assistance, which is not too bad considering the ferocity of the storm," Greg Murphy, the NSW SES deputy operations controller said.

"The outlook is for more storms perhaps tonight and into the weekend, so we may have more to come."

NSW's TOP RAINFALL TOTALS OVERNIGHT

Mona vale - 121mm

Terrey Hills - 72mm, including 42mm in just 30 mins up to 8.45pm

Kings Langley - 66mm

Murrays Flat (near Goulburn) - 82mm in two hours up to 3.30pm.

Meanwhile, a separate heavy storm system also drenched south-east Queensland overnight.

The Bureau of Meteorology warned yesterday of the “very dangerous cell” that crossed over areas ranging from Warwick and Beaudesert up to Kingaroy, Gympie and Rainbow Beach.

Beaudesert was one of the worst-hit locations in the region, receiving 66mm of rain throughout the night and 41mm of that in just a 10-minute window.

Blackbutt, north-west of Brisbane, also had 70mm of rain fall during the storms.

The BoM has predicted a moderate chance of rain and thunderstorms again today for northern and eastern parts of Queensland, as well as gusty winds and heavy showers for the south-east.

Golf ball-sized hail stones were seen falling from the sky in parts of Sydney, including Mona Vale in the north which received up to 120mm of rain. (Supplied/Amy Lyall)

The storms began around lunchtime along the coast, dropping large amounts of hail in both cities. (Supplied)

AROUND THE COUNTRY

Canberra: Partly cloudy with light winds and 26C weather before a cooler change leading into the weekend.

Melbourne: Mostly sunny throughout the day with some fog in the morning and 23C. Expected to warm up over the weekend and into next week.

Hobart: Cooler day with temperatures in the low-20s and some light winds and cloud until early next week, when some rain could pass over Tasmania.

Adelaide: Clear skies expected for coming days as the temperatures rise into the 30s, despite some light winds.

Perth: Hot and sunny weather from today until Monday, when some cloud cover should pass over. Temperatures in the low- to mid-30s.