Sydney-siders are in the path of a massive line of storms expected to hit the city’s western suburbs by school pick-up time.

The weather band is part of a line of slow-moving thunderstorms expected to bring an increased risk of flash flooding across a broad area of south-eastern Australia on Thursday, with the ACT and Victoria also in the firing line.

“An active line of heavy showers and thunderstorms [is] moving towards Sydney,” the Bureau of Meteorology wrote on X at 2.30pm (AEDT).

“The storm will reach the far western suburbs shortly.”

Tweet from @BOM_NSW

It was accompanied by a radar image of a wide band of storms stretching from Scone, about 270 kilometres north of Sydney, to Batemans Bay on the NSW south coast.

The weather bureau has also issued a warning for severe thunderstorms that are likely to produce heavy rainfall that may lead to flash flooding in Wollongong, Nowra, Bowral, Mudgee, Katoomba and Dubbo.

There was also a detailed storm after severe thunderstorms were detected on the weather radar near Colo Heights and the Wollemi National Park north of Kurrajong.

“These thunderstorms are moving towards the east,” BOM said.

“They are forecast to affect Wilberforce, the Yengo National Park northwest of St Albans and Cattai by 3.05pm and Glenorie, Maroota and Wisemans Ferry by 3.35pm.”

The NSW SES tweeted its own warning to residents in the path of the storms.

“Severe thunderstorms may bring flash floods. Keep out of floodwater and prepare your home now,” it said.

Forecaster Weatherzone said earlier that there were large storms in north-eastern Victoria and southern NSW “as the sun rose on Thursday”.

“A moisture-laden air mass interacting with an upper-level trough will create an ideal environment for towering clouds and thunderstorms on Thursday,” it said.

“Lightning should become more widespread throughout the day and into the evening as warmer air near the surface further fuels this storm-ripe environment.”

Weatherzone said some inland regions of NSW had already had good rain totals. They included Albury, on the NSW-Victoria border, which broke a three-week dry spell with 41 millimetres of rain.

Braidwood, east of Canberra, had its heaviest daily rainfall in a year with 31.6 millimetres on Wednesday.

“Thursday’s wet and stormy weather is part of a prolonged storm outbreak that has been affecting eastern Australia since late last week, fuelled by humid easterly winds and a series of low pressure troughs,” Weatherzone wrote.

A detailed thunderstorm has been issued for parts of the Blue Mountains. Image: BOM

Much of Victoria has been put on heightened alert for thunderstorm asthma this week, with widespread storms combining with high-to-extreme pollen levels to raise the risks.

Some of the state’s hospital emergency departments have also reported spikes in asthma-related presentations. More than 200 people presented with asthma-related symptoms between 4pm Tuesday and 2.30pm Wednesday – five time the usual number.

Melbourne was the scene of the world’s worst thunderstorm asthma event in 2016, when a wild storm brought conditions that left 10 dead and thousands of others seeking emergency help.

Weatherzone said more than a million lightning strikes were detected over Queensland and NSW last weekend, with hail and heavy rain in parts of Victoria by Tuesday.

Storms become more widespread on Wednesday, with lightning occurring over part of every state and territory in the afternoon.

Weatherzone said showers and storms would continue for several Australian states and territories for the rest of this week and into early next week.