Peak-hour chaos for Sydney after intense thunderstorm smashes trains, airport

Sydneysiders are facing peak-hour chaos following a massive thunderstorm that caused widespread power outages, leading to flight, train and traffic delays.

On the rail network, trains have started running again after a long outage on the T1 North Shore and Western Line after lightning damaged signalling equipment at Milsons Point.

That's causing significant flow-on effects across the city, with trains delayed on most of the other lines.

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Replacement buses are still now operating, but commuters have been advised to allow "plenty of extra travel time" or find alternate transport options for the trip home.

There are problems on Sydney's roads as well, with flooding causing closures in Alexandria and a burst water main impacting traffic in Darlinghurst.

Earlier in the afternoon, the main runway at Sydney Airport was closed for 20 minutes after it was struck by lightning, opening up a hole in the tarmac.

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While it was repaired by crews in less than half an hour, departures and arrivals at Sydney Airport are delayed by about 65 minutes on average.

Planes bound for Sydney were grounded interstate, unable to take off until other flights were cleared. 

Passengers were encouraged to check with their airline regarding the status of their flight.

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Lightning strikes

The city and surrounds were hit by about 75,000 lightning strikes in three hours from 10am as the severe thunderstorm rolled through.

Four people were hospitalised after the tree they were sheltering under at the entrance to the Royal Botanic Garden was struck by one of the strikes just before 1pm.

A 19-year-old man and a 20-year-old woman were transferred to RPA Hospital while a 36-year-old man and a 36-year-old woman were taken to St Vincent's Hospital.

Supermarkets in Balgowlah and Manly Vale lost power after the area was hit by a large number of lightning strikes.

Flash flooding warning

About 27mm of rain fell at the airport in three hours, 28mm fell at Gosford and 25mm fell at Badgery's Creek.

Earlier, the State Emergency Service (SES) warned those in low-lying areas in eastern parts of the state to monitor flooding.

NSW SES Assistant Commissioner Sean Kearns said there was potential for isolated heavy falls of 50mm to 100mm throughout this afternoon.

"The NSW SES has prepositioned personnel throughout the region, and we are well-resourced to respond to any calls for assistance," Kearns said.

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The Bureau of Meteorology warned the severe storm would bring heavy rainfall that may lead to flash flooding.

Flash flooding was detected at Wyong, Tuggerah and Randwick.

The worst of the storm hit the CBD, Sydney Airport and the Sydney Harbour Bridge by 1.05pm and Gosford, Ryde and Swansea by 1.35pm.

"A more general severe thunderstorm warning is also current for parts of the Mid North Coast, Hunter, Metropolitan, Central Tablelands, North West Slopes and Plains, Northern Tablelands, Illawarra and Central West Slopes and Plains districts," the BoM said.

Emergency services are warning people not to drive or walk through floodwaters.