Total fire bans have been issued in NSW and Victoria ahead of another worrying burst of summer heat.

NSW started 2021 with torrential rain but soaring temperatures will scorch much of the state from Wednesday.

A high-pressure system over the Tasman Sea is drawing warmer air across NSW, with the Bureau of Meteorology forecasting temperatures to hit the high 30s and lows 40s.

Southern NSW and the Riverina are already feeling the heat but it will build and spread across the state, likely until Friday.

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“We’ll see temperatures in Wagga Wagga [reach] 41 on Wednesday, the hottest time of the week for that area, [and] Griffith 42,” meteorologist Melody Sturm said.

“Those are both about nine degrees above the January average.”

The nights won’t bring much relief either, with temperatures forecast to remain high.

With the heat comes heightened fire danger across the state.

The Riverina is the subject of a very high danger rating that will extend until Thursday.

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The ACT will also swelter this week, with Canberra expected to reach 36 degrees.

South of the border, Victoria has issued total fire bans for the Mallee, Wimmera and northern country districts, with hot, dry and windy conditions forecast for Wednesday.

Temperatures are expected to soar back into the high 30s and low 40s in the far north-west on Wednesday, including 41 degrees at Mildura, after Monday’s scorching conditions eased.

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The Country Fire Authority says fire danger in those districts is considered severe – the same rating as on Monday – and very high to high in other areas of Victoria.

On Monday, a grass fire at Taylors Hill in Melbourne’s outer north-west threatened homes, rising to watch and act level before being brought under control.

CFA chief officer Jason Heffernan said grassfires that broke out were successfully managed but he was disappointed to learn of several deliberately lit fires.

“We saw campfires lit in places along the Murray River, near Myrtleford and Apollo Bay, on a day of very hot and windy conditions,” he said on Tuesday.

“There were also a number of backyard bonfires in residential areas, which is really disappointing on such a hot day.”

Campers and harvesting farmers have been urged to take care and adhere to Wednesday’s total fire ban, which outlaws open-air fires from 12.01am to 11.59pm.

Meanwhile, South Australian police are investigating the cause of a major grass fire that threatened a small community in the state’s south-east.

The fire burnt through 16,800 hectares at Lucindale, including into the town. There are no confirmed losses of houses or major structures.

Livestock and fencing have been destroyed and more than 3000 properties are without power.

The Country Fire Service has reduced the alert level to a bushfire advice but still has crews in the area strengthening containment lines.

About 45 fire trucks and 200 firefighters were deployed at the height of the fire.

Water bombing aircraft conducted more than 100 drops across the fire ground and were expected to continue their work on Tuesday.

The fire was fanned by strong winds with a cool change pushing it towards Lucindale and Naracoorte.

CFS Duty Commander Brenton Hastie said the fire grew rapidly and changed shape as the cool change moved through.

“We don’t have any confirmed losses at this stage, but we are aware of a number of properties that have been impacted,” he said.

The fire came amid dangerous conditions across much of SA on Monday, with very high temperatures and rising winds.

Cooler conditions prevailed across the fire ground on Tuesday with temperatures in the mid-20s forecast for the rest of the week.

-with AAP