A FIREFIGHTING aircraft is en-route to Delburn in Gippsland, Victoria, as fire crews battle the third blaze in the area in 24 hours.

A CFA spokesman said two fires had ignited in the area since noon today, after another fire burnt out 30ha of private land overnight.

The spokesman said the first fire, visible from the Strzelecki Highway, was now listed as "safe'', meaning it can be left without further patrol.

• Temperature soar into the 40s ... again

The second fire is burning in scrub near a pine plantation.

Five fire trucks are currently battling the fire.

"We've got an aircraft on the way to that one,'' the spokesman said.

"We're pretty keen to knock it on the head before it gets into the pine plantation.''

Two fires are also burning at Drummond North near Malmsbury in central Victoria.

One fire is on public land and is being fought by Department of Sustainability and Environment fire crews.

The CFA is battling the second, smaller fire, which is causing a lot of smoke in the area.

The CFA spokesman said fire activity in Victoria had increased significantly "in the last couple of hours''.

"It is likely to get worse as the afternoon progresses,'' he said.

Meanwhile, temperatures continue to climb across southeastern Australia, with the mercury above 40C in western, central and southeastern Victoria.

In Gippsland, temperature gauges at Bairnsdale peaked at 42.5C at 12.53pm, while the Latrobe Valley reached 42.8C at 1.20pm.

In the Wimmera, Longerenong is sweltering at 42.3C, while Horsham, Nhill and Stawell are all above 41C.

Temperatures at Casterton, Hamilton, Mortlake, Kyabram, Shepparton and Yarrawonga remain above 41C.

The mercury reached 43.5C in Melbourne at 2pm.

Many farmers in the state's north have shelved outdoor jobs in favour of watching the Australian Open on TV to escape the heat.

Corowa grain grower Roly Dye said watching the tennis between lunch and 4pm was on the agenda, followed by farm chores.

"We are desilting dams at the moment and try to get our jobs done in the mornings when it is cooler,'' he said.

"The stock have been holding up in the heat.''

In the northeast, the heat has dried up stock dams on the Tungamah farm owned by Joe Lawless.

"Yesterday it got to 42C and I was pulling sheep out of dams,'' he said.

"Not pleasant, but the kids had a lot of fun.

"I watch the tennis in the afternoons and then go out at 6pm to do another few hours, such as moving a bit of hay (for stock).''

Residents in Adelaide have fared a little better today, with the temperature hovering around 42C this afternoon - slightly better than yesterday's top of 45.5C.

But farmers in the state's southeast continue to swelter, with temperatures remaining above 43C at Keith, Mount Gambier and Naracoorte.