Sydney braces for severe thunderstorms - Sydney Morning Herald

The Bureau of Meteorology is warning Sydney to brace for severe thunderstorms for the next few hours.

Large hailstones, heavy rainfall that may lead to flash flooding and damaging winds are likely.

The State Emergency Service says people should move their cars away from trees, secure loose items around their house and keep clear of fallen power lines and drains.

Bureau duty forecaster Dmitriy Danchuck said the storm would hit quickly.

"It is probably a few small cells grouped together, and they are bringing heavy rainfall, some hail and reports of wind-gusts as well," he said. "Storms are expected to affect Sydney for the next few hours".

He said lightening strikes were also a possibility, with active lightening all across north-eastern NSW.

"It stretches all the way from the Queensland border towards Sydney, and that will create constant thunderstorms for the next few hours," he said.

The Bureau said the severe storms have already been detected on the radar between Richmond and Riverstone, and are expected to hit Dee Why, Terrey Hills and waters off Bondi Beach by 1:15pm.

A general severe thunderstorm warning is also currently in place for the Hunter, Metropolitan and parts of the Mid North Coast, Illawarra, Central Tablelands, North West Slopes and Plains, Central West Slopes and Plains and Northern Tablelands districts.

Meanwhile, Sydney is still recovering from storms that have wreaked havoc of the past 24 hours.

Release of untreated sewage into the Georges River has prompted NSW Health to advise people and their pets to avoid all contact with the river from Macquarie Fields to Botany Bay for the next 48 hours to include swimming, sailing, canoeing and fishing.

The water in the river is likely to pose a serious risk of gut and skin infections, Syney Water said. Anyone who does come into contact with the water should wash themselves carefully, and seek medical advice about any open wounds that may have been exposed.

In a statement the company said that as a result of heavy rainfall and flooding in the Campbelltown area since yesterday, a flow of untreated wastewater was occurring from the Glenfield Wastewater Treatment Plant into the Georges River.

It said the intensive downpour flooded the inlet pumping station at the plant last night which resulted in the pumps being unable to operate causing release of untreated wastewater into the river.

Crews have worked throughout the night and are currently attempting to pump the wastewater into the plant for treatment using generators and portable pumps.

It added: "Sydney Water is also undertaking water quality testing, Sydney Water advised NSW Health, NSW EPA Campbelltown and Liverpool Councils of the incident last night and will continue to work with the relevant agencies to resolve the situation today."