Teen charged over grassfire as crews warn to prepare for 'catastrophic danger'

The record-breaking heat is expected to continue in northern New South Wales and Queensland on Sunday, with catastrophic fire danger warnings being issued as the mercury continues to soar.

The warnings come as police confirmed a teenage boy has been charged, after allegedly lighting a fire in NSW’s Central West.

NSW Police said the 13-year-old boy was arrested on the outskirts of Orange after witnesses allegedly saw him starting a grass fire on Saturday night.

The boy was taken to Orange police station and charged with destroying property and setting fire to the property of another.

He was granted bail and is set to appear in Children’s Court on Monday.

Police alleged no buildings were damaged in the fire however approximately 100 vehicles were.

HOT! HOT! HOT! Where the heatwave will strike today

Brisbane: 39C
Birdsville (Qld): 47C
Warwick (Qld): 46C
Tamworth (NSW): 44C
Moree (NSW) 46C
Bourke (NSW) 47C

NSW: 'This is as bad as it gets'

As a cooler change blows into Sydney, much of NSW is facing the most catastrophic fire danger in history as a monster hot air mass continues north.

While temperatures aren't even tipped to reach 30C in Sydney on Sunday, much of NSW will remain above 40, as fire dangers reach unprecedented levels.

"To put it simply, they're simply off the old conventional scale," Rural Fire Service Commissioner Shane Fitzsimmons said on Saturday.

"It's not another summer day, it's not another bad fire weather day. This is as bad as it gets."

Catastrophic conditions are forecast for the Greater Hunter, Central Ranges and North Western area.

Towns in northern NSW are set to cop the brunt of the hot air mass moving north towards Queensland.

Tamworth is forecast to reach 44C and Moree 46C, while Walgett and Bourke could reach a sweltering 47C.

Firefighters were battling a bushfire east of Dunedoo, on Saturday night, prompting a watch and act alert for residents of Uarbry and Cassilis.

QLD: Mercury to keep rising until Tuesday

A record setting heatwave sweeping southern Queensland is only set to intensify.

While temperature records were sent tumbling on Saturday, the Bureau of Meteorology said the mercury would keep rising through Sunday.

"It's looking like the hottest of the lot, we should see quite a few more records fall and a lot of places that were hot on Saturday even hotter on Sunday," BOM forecaster Dean Narramore told AAP.

"We saw on Saturday an incredible amount of records broken in NSW and that heat is just moving north for Sunday."

Four Queensland towns set their highest ever recorded temperatures on Saturday as Brisbane reached 37C.

The city is tipped to reach 39C on Sunday, while several towns in southwestern Queensland, including Birdsvillle, could hit 47C.

The state record for hottest February day stands at 46.5C, while Birdsville's hottest February maximum is 46.2C.

A number of heat records tumbled on Saturday, with Warwick, Applethorpe and Oakey all having their hottest ever days.

Paramedics have urged people to keep hydrated to avoid becoming ill as temperatures push more than 10C past the February average.

They've suggested swapping caffeinated drinks for water, eating small and regular meals and wearing light-coloured cotton clothing.

As people flocked to the coast for a reprieve from the heat, rough surf led to dozens of rescues and the closure of several beaches on the Gold Coast and Sunshine Coast on Saturday.

Lifesavers will assess beaches Sunday morning before the worst of the heatwave hits.

Relief from the heat isn't expected until Tuesday following the arrival of a southeasterly change.

WA: Perth hit by record rainfall

The Swan River in Perth is expected to peak at 1.6 metres early on Sunday as the runoff from the flooded Wheatbelt region reaches the city.

Torrential rain swelled rivers and washed away roads across WA on Saturday, with the state's Wheatbelt and Goldfields hardest hit, while Perth received its second highest rainfall on record on Friday, with more than 114mm raining down on the city.

A severe weather warning, however, has now been cancelled for the Great Southern region.

Flood water enveloped the Phillip River Bridge on the South Coastal Highway near Ravensthorpe on Saturday afternoon, leaving 15 people from six vehicles stranded.

WA's Fire and Emergency Services said they contracted a private pilot of a small helicopter to rescue a group.

Flooding hit the community of Toodyay, along Stirling Terrace, and Mortlock River East at O'Driscolls Farm.

Water levels within the Avon River catchment were expected rise over the weekend and moderate flooding was also expected along the river in Beverley.