Severe storms have swept over Australia, providing relief for crews tackling raging wildfires but bringing threats of flash floods, landslides and water pollution.

Forecasters said the “much-needed” downpours could help extinguish some of the 114 blazes across New South Wales (NSW) and Victoria states, where hot and dry weather has helped fuel the country’s worst bushfire season on record.

Some fire-ravaged areas of eastern Australia could see 50mm to 100mm of rain over the next few days, said the country’s Bureau of Meteorology.

“If this rainfall forecast comes to fruition then this will be all of our Christmas, birthday, engagement, anniversary, wedding and graduation presents rolled into one. Fingers crossed,” tweeted NSW’s rural fire service.

But forecasters warned heavy rain brought the risk of flash flooding and landslides, particularly in burnt-out areas. The downpours could also pollute fresh water supplies if debris is swept into reservoirs.

“This is a day that we are quite concerned about,” said Kevin Parkyn, a senior meteorologist at the bureau. “Thunderstorms are a bit of a double-edged sword. While they can bring some much-needed rain, it can also come down in very fast, high quantities.”

Animals rescued during Australia fires Show all 25 1 /25 Animals rescued during Australia fires Animals rescued during Australia fires Wildlife rescuer Simon Adamczyk is seen with a koala rescued at a burning forest near Cape Borda on Kangaroo Island, southwest of Adelaide AAP Image/Reuters Animals rescued during Australia fires Rural Fire Service volunteer firefighter Pat Smith pouring water onto a possum's feet with burns from fires on the outskirts of the town of Tumbarumba in New South Wales Greenpeace Australia-Pacific/AFP Animals rescued during Australia fires Wildlife Information, Rescue and Education volunteer and carer Tracy Dodd holds a kangaroo with burnt feet pads after being rescued from bushfires in Australia's Blue Mountains area Reuters Animals rescued during Australia fires Grey-headed Flying Fox bats prepared for a feeding at the Uralla, Australia, home of Jackie Maisey, a volunteer with Northern Tableands Wildlife Carers. The bats are swaddled in flannel wraps similar to those being made by thousands of crafters worldwide who are using their sewing, knitting and crocheting skills to make items for wildlife injured in the Australian brush fires Jackie Maisey/AP Animals rescued during Australia fires Sara Tilling takes care of a young injured Kangaroo which she and her partner Gary Henderson are nursing back to health in Cobargo EPA Animals rescued during Australia fires Humane Society International Crisis Response Specialist, Kelly Donithan holds a baby Koala she just rescued on Kangaroo Island AFP via Getty Images Animals rescued during Australia fires Tracy Burgess holds a severely burnt brushtail possum Reuters Animals rescued during Australia fires Fire-impacted, orphaned pouch-rescued Eastern Grey Kangaroo joeys are seen at the property of WIRES Carers Kevin and Lorita Clapson in East Lynne, South of Sydney EPA Animals rescued during Australia fires A koala receives water from a cyclist during a severe heatwave that hit the region, in Adelaide Instagram/BIKEBUG2019 via Reuters Animals rescued during Australia fires An orphaned Flying-Fox is fed at the property of WIRES Mid-South Coast Bat Coordinator, Janet Jones, in Tuross Head EPA Animals rescued during Australia fires Humane Society International Crisis Response Specialist, Kelly Donithan checks an injured Koala she had just rescued on Kangaroo Island AFP via Getty Animals rescued during Australia fires A wallabie eating a carrot dropped by the NSW National Parks and Wildlife services over the bushfire affected areas along the South Coast for wallabies NSW National Parks and Wildlife Services Animals rescued during Australia fires A dehydrated and injured Koala receives treatment at the Port Macquarie Koala Hospital AFP via Getty Animals rescued during Australia fires Gary Henderson holds the young injured kangaroo he and his partner are nursing back to health EPA Animals rescued during Australia fires A koala drinks water offered from a bottle by a firefighter during bushfires in Cudlee Creek, south Australia Oakbank Balhannah CFS via Reuters Animals rescued during Australia fires WIRES Mid South Coast wombat coordinator Tony De La Fosse with two orphaned pouch-rescued Wombats at his property in Malua Bay EPA Animals rescued during Australia fires Qantas, an orphaned Eastern Grey Kangaroo joey whose feet were burned in recent bushfires, is held by WIRES Carer Kevin Clapson at his property in East Lynne EPA Animals rescued during Australia fires Various completed animal pouches for animals affected by Australia bushfires hang on clothing racks in Regents Park, Queensland Kim Simeon via Reuters Animals rescued during Australia fires An orphaned pouch-rescued Eastern Grey Kangaroo joey hangs in a makeshift pouch at the property of WIRES EPA Animals rescued during Australia fires A rescued koala injured in a bushfire in Kangaroo Island, South Australia Kangaroo Island Wildlife Park/AP Animals rescued during Australia fires WIRES Mid-South Coast Bat Coordinator Janet Jones weighs a rescued Grey-Headed Flying-Fox at her home in Tuross Head EPA Animals rescued during Australia fires A weary kangaroo shelters on a patch of green grass surrounded by burnt bushland along the Princes Highway near in Milton Reuters Animals rescued during Australia fires Various animal wraps for bats affected by bushfires Simone Watts via Reuters Animals rescued during Australia fires A staff member moving a rescued koala to a temporary shelter at the Taronga Zoo in Sydney Taronga Zoo/AFP via Getty Animals rescued during Australia fires A kangaroo jumps in a field amidst smoke from a bushfire in Snowy Valley AFP via Getty Images

The storm’s strong winds could also increase the risk of falling trees, already weakened by fire, warned Sarah Scully, an extreme weather forecaster with the bureau.

Last week, firefighter Bill Slade, 60, was killed by a falling tree near Omeo, southeastern Victoria. His death was the 28th confirmed fatality linked to the bushfires, which have raged for months.

That death toll has since increased to 29, after Victoria state officials said this week that a fire management contractor killed in a car crash in November was now being classed as a victim of the blazes.

The family of a 19-year-old who died after suffering an asthma attack in Glen Innes, a town in NSW, have also blamed her death on smoke from the wildfires, though preliminary autopsy reports listed her cause of death as unconfirmed.

Hospital admissions have increased in smoke-affected cities, with some patients suffering from asthma for the first time in their lives. The government has responded by distributing 3.5 million free particle-excluding masks, and acting chief medical officer Paul Kelly said there were plans to launch a study of the long-term health implications of the wildfire smoke.

Fire alarms have been sounding in high-rise buildings in Sydney and Melbourne as dense smoke from distant wildfires confuses electronic sensors, while government offices in the capital Canberra have shut because the air inside is too dangerous for civil servants to breathe.

Australian Open organisers delayed the start of tennis matches by two hours on Wednesday as they waited for smoke to clear on the second day of qualifying. Smoke and hazy conditions at Melbourne Park affected the opening day’s play and several players criticised the tournament for allowing matches to go ahead.

More than 2,500 homes have been destroyed by the wildfires, which have razed bushland across an area the size of Bulgaria since September and killed a billion animal including koalas, kangaroos and bats.