Firefighters have taken advantage of less extreme conditions to try to contain blazes burning across New South Wales ahead of worsening conditions and soaring temperatures expected on Tuesday.

More than 100 fires were still burning across NSW on Sunday, including the massive Gospers Mountain blaze, which is expected to burn for weeks.

Meanwhile, on Kangaroo Island, a bushfire burning at Newland was also posing a threat to lives.

Amid the ongoing bushfire crisis, which has claimed six lives and more than 1,000 homes, the federal opposition restated its call for an emergency Council of Australian Governments meeting to discuss a national response to the bushfire emergency.

Conditions eased on Sunday as a result of slackening winds and more moisture in the air, which allowed fire crews to conduct backburning before conditions deteriorate again.

Monday will bring very high fire danger for parts of the state as temperatures build again toward heatwave conditions the Bureau of Meteorology (Bom) has forecast for Tuesday.

Victoria has also declared a total fire ban for some parts of the state on Monday ahead of very high temperatures and strong winds.

In Queensland, conditions also eased on Sunday morning but were flaring again by the afternoon.

A prepare to leave warning was issued for the West Kinkuna/Goodwood bushfire on Sunday afternoon.

On Tuesday, a number of districts in southern and central NSW – including the Greater Hunter, the southern and central ranges, and the Illawarra and Shoalhaven regions – are expected to experience severe fire danger. Temperatures in some parts of the state, including western Sydney, will soar into the 40s.

The Bom said some inland areas, such as Bathurst and Orange, could see record temperatures for December.

“It looks likely we’ll see the next big peak day on Tuesday, with a number of districts likely to experience severe fire danger,” Bom meteorologist Diana Eadie said.

“We’ll see another wind change move across the area, we’ll see winds ahead of that change strengthening in combination with very warm temperatures and dry conditions.”

Eadie said that because the fires across the state were now so large, severe conditions of the kind expected on Tuesday could intensify the situation.

By Wednesday and Thursday, she said, the focus would shift again to north-eastern parts of NSW where fires have been burning for weeks. She said westerly winds could also again increase the smoke haze around areas such as Sydney later in the week.

The NSW Rural Fire Service commissioner, Shane Fitzsimmons, told Seven News that crews working to contain fires on Sunday had been dealing with “more benign” conditions across most of the fire grounds compared with previous days.

“Which means hundreds – as a matter of fact more than 1,600 – firefighters are around again today doing really important and critical backburning and containment line consolidation to try and gain the upper hand before we see those conditions deteriorate into Tuesday.”

However, despite the easing conditions, many firefighters were still up against hard-to-control blazes, including the Green Wattle Creek blaze, south-west of Sydney.

Victoria’s Mallee, Wimmera and Northern Country districts will be under a total fire ban on Monday, with very high to severe fire danger expected.

Gusts of up to 70km/h are also forecast for the north-west, with an expected high of 43C in Mildura and 42C in Swan Hill.

Melbourne is forecast to reach a top of 39C.

In Queensland, a high fire danger rating was in place on Sunday for the Darling Downs and Granite Belt to Cape York Peninsula, and severe fire danger was forecast for the Northern Goldfields and Upper Flinders on Monday.

Late on Sunday the Kangaroo Island blaze at Harriet Road was uncontrolled while burning under severe weather conditions. An emergency warning had been issued and residents were advised to leave without delay or seek shelter.

Total fire bans were also in place in 14 other regions around South Australia. Two other bushfires were burning on the lower south-east region.

The Labor senator Murray Watt said a bipartisan response was necessary to prepare Australia for the coming bushfire season, with the east coast already experiencing what has been labelled “unprecedented” catastrophic fires.

“Last week we met with ex-fire chiefs who, with decades of experience saving lives and fighting fires, are ready to help,” Watt said. “Their advice was clear – we will see more natural disasters due to our changing climate and we are not ready to deal with it.

“Labor once more urges this government to call an urgent Coag meeting, to ensure Australia has the water-bombing aircraft, volunteer incentives and other measures necessary for the future.”

Speaking to the ABC’s Insiders program, the government’s leader in the Senate, Mathias Cormann, said the government was responding as needed.

“If and when additional support is required, then, of course, we would consider that, but right now as we speak, you know, we obviously planned for this bushfire season and we have put significant measures in place and we have put significant measures in place for the future too, to better address, you know, these sort of emergencies into the future,” he said.

The home affairs minister, Peter Dutton, also dismissed independent MP and former infantry officer Andrew Wilkie’s request for airforce transport planes to be deployed for water-bombing, saying there were a lot of “armchair experts in this space”.

“It may be that it’s more efficient to engage purpose-built aircraft that we contract in over the summer or over the period we’re under most threat,” Dutton said during a Sky News appearance.

“The experts including the defence experts make those calls and government will take that advice.”

Over the weekend, leading climate scientists criticised the government for its silence on the climate crisis while the fire emergency continues to unfold.

• Australian Associated Press contributed to this report