Australia Day scorcher: The weather and events happening in your city

Australia Day is set to be a scorcher across most of the country as residents prepare for festivals, parades and citizenship ceremonies.

Throughout Friday, half a million people are expected to flood Sydney to celebrate the national day and the mercury is set to hit 29 degrees with a chance of showers in the outer west.

Adelaide is expecting the city's hottest Australia Day since 2006 with a top of 37 and Melbourne residents are preparing for a hot and humid Friday at 29 degrees.

Citizenship ceremonies and backyard barbecues are bound to draw big crowds, but not all will be celebrating this year.

Thousands are expected at "Invasion Day" marches around the country, with more than 5000 expected at a rally outside the Victorian Parliament, and similar numbers preparing to walk in Sydney, starting from The Block in Redfern.

Here's your guide to what's happening across the country for Australia Day.

Sydney

Sydney Harbour will be awash with festivities throughout Australia Day, culminating in a spectacular fireworks display.

About half a million people are expected to flock to the city to celebrate Australia's national day, with scores of extra police on hand to keep an eye on revellers.

Meanwhile, indigenous performers including the Koomurri Aboriginal Dancers will perform at Walumil Lawns around 8.30am and the KARI Singers will sing the national anthem in English and Dharawal on the Sydney Harbour Bridge.

The harbour will be bustling with ships and ferries including the HMAS Canberra and a 21-gun salute will be fired from Bradfield Park in North Sydney around midday.

A fleet of yachts, tugboats, jetskis and ferries are then set to perform an aquatic ballet, manoeuvring in unison to classical music on the harbour.

A spectacular fireworks finale featuring a musical medley of Australian classics will light up the harbour to finish the celebrations in the city.

Despite planned industrial action on Sydney's rail network being postponed, Transport NSW has warned commuters to expect some delays.

Melbourne

A fine 29 degrees is forecast and crowds are expected to line to Swanston Street from 11am for the Australia Day parade, with more than 1000 participants from Melbourne's varied cultural groups taking part.

Among them, adding a flourish of colour and panache, are beauty queen contestants vying for the titles of Miss Gay and Miss Transsexual Australia.

Aboriginal academic and female impersonator Harley Dunolly-Lee, 27, will be part of the group for the first time - going under the stage name Ana Diction.

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A flag raising ceremony will be held outside Melbourne Town Hall at 10.30am, with dignitaries including Premier Daniel Andrews attending.

In the afternoon, Aboriginal artists are set to showcase music at a festival in Treasury Gardens and a family festival will held in the Kings Domain Gardens.

A fireworks display from the Docklands Harbour Espalande will cap off the day.

Authorities say they'll be on high alert with 'invasion day' protesters set to rally outside Parliament House and a far-right group due to gather at St Kilda.

The day's activities come after three Melbourne councils - Darebin, Moreland and Yarra - dumped Australia Day out of respect to indigenous people.

Following the move, the federal government revoked Darebin and Yarra's ability to host citizenship ceremonies at any time of the year.

Adelaide

Australia Day is set to be a scorcher in Adelaide with partygoers warned to take it easy.

The mercury will reach a high of 38C on Friday in Adelaide rising to 42C on Saturday and Sunday, the Bureau of Meteorology says.

It's likely to be the hottest Australia Day since 2006 when the top was 41.1C.

"It becomes quite a serve heatwave event for the period Friday, Saturday and Sunday," the bureau's regional director John Nairn said.

The regional centre of Coober Pedy is tipped to reach 44C, Roxby Downs 45C and Ceduna 39C on Australia Day.

Some events have been cancelled including the City of Salisbury's family picnic.

Other events have been moved indoors.

But the traditional Australia Day parade and Elder Park concert are expected to go ahead as planned.

Brisbane

Brisbane Lord Mayor Graham Quirk is set to officiate what's billed as the largest citizenship ceremony in the country on Friday morning, with 600 people set to become New Australians.

Premier Annastacia Palaszczuk will be in Townsville to attend the annual flag-raising ceremony in the city, as well as a citizenship ceremony.

"People are going to be celebrating what is great about Australia, and I believe that is our willingness to be inclusive," Ms Palaszczuk said in Townsville on Thursday.

Brisbane will also see the annual cockroach races at the Story Bridge Hotel, which has been running since 1982.

In addition to celebrations, those opposed to holding Australia Day on January 26 have organised a rally to be held in Brisbane's Musgrave Park, with a march planned to the state parliament building.

Rain could put a dampener on proceedings across the state, with a high of 31 degrees predicted for Brisbane, and northern parts of the state expected to see heavy rain continue.

Hobart

Ferret races and a strongman competition headline Australia Day festivities in northern Tasmania, while hundreds are expected to rally in the state's south for a date change.

The lawns of Hobart's parliament house mark the endpoint for the march, held in conjunction with national protests in opposition to the January 26 public holiday.

A second rally is planned for Devonport.

Meanwhile, revellers expected to flock to beaches and parks around the Apple Isle are being warned to brace for a "heatwave" across the long weekend.

A temperate 27 degrees is forecast for Hobart on Friday before the mercury hits 36 on Sunday.

Perth

About 300,000 people are expected to jostle along the Perth foreshore on Australia Day for the best view of the City of Perth's Skyworks show finale at 8pm, boasting the nation's largest Australia Day fireworks display.

The Skyworks show broadcast, which begins at 3pm, will feature the Birak indigenous concert at the Supreme Court Gardens and there will be an entertainment zone at Langley Park.

Limited alcohol can be consumed at two BYO licensed areas at Langley Park and Kings Park.

The forecast is a sunny 30C with evening temperatures a balmy 18C.

Citizenship ceremonies will also be held by local councils across the state, including free events and barbecues.