Australia's Prime Minister Scott Morrison, with NSW Premier Gladys Berejiklian, left, speaks to the media during a visit to the Wollondilly Emergency Control Centre in Sydney, Sunday, Dec. 22, 2019. Morrison on Sunday apologised for taking a family vacation in Hawaii as deadly bushfires raged across several states, destroying homes and claiming the lives of two volunteer firefighters. (Joel Carrett/AAP Images via AP)

Sydney - Australian Prime Minister Scott Morrison apologised on Sunday for his decision to take an unannounced family holiday to Hawaii in the midst of a bushfire emergency and record-breaking heat.

Morrison came back on Saturday night, having decided to cut his trip short after widespread public criticism and the deaths of two firefighters who were killed battling a "horrendous" blaze south-west of Sydney.

"I have returned from leave and I know that [my holiday] has caused some great anxiety in Australia," Morrison said in a press conference Sunday morning, adding that with "the benefit of hindsight" he would have acted differently.

"I am sure Australians are fair-minded and understand that when you make a promise to your kids you try and keep it," Morrison said. "But as prime minister, you have other responsibilities, and I accept that and I accept the criticism."

The prime minister's office was also heavily criticised for declining to confirm Morrison's whereabouts during the bushfire crisis, which triggered a second state of emergency in New South Wales (NSW) on Thursday.

The hashtags #WheresScotty and #Morrisonfires trended on Twitter in Australia this week, and a student protest was staged at Morrison's Sydney residence.

"Thank you for doing nothing in Australia and holidaying in Hawaii," one of the young protesters said in Facebook Live video posted by rally organizers Schools Strike 4 Climate.

Upon his return, Morrison said that he can "accept the criticism."

"For those Australians I caused upset to, I apologise for that," he said.

This week, Australia experienced its hottest days on record with the Bureau of Meteorology recording a national average temperature of 41.9 degrees Celsius on Wednesday and 41.0 degrees on Thursday.

At Sunday's press conference the conservative prime minister also addressed climate change, as the government faces pressure to take more action.

"There is no argument about the links between... broader issues of global climate change and weather events around the world," Morrison said.

"But I'm sure people equally would acknowledge that the direct connection to any single fire event - it's not a credible suggestion to make that link." 

Both South Australia and New South Wales revealed devastating figures due to bushfires over the past three days. 

South Australia's Premier Steven Steven Marshall told reporters on Sunday evening that at least 72 homes had been destroyed in the Cudlee Creek fire which started Friday. Some 400 sheds and outbuildings and 227 vehicles were also destroyed in the fire.

25,000 hectares have already burned, while 300 firefighters are battling the areas still burning.

Two people died in South Australia, which saw 49 degrees Celsius heat this week, while the smoke from the blaze dropped the city's air quality to poor on Sunday. 

In New South Wales, Premier Gladys Berejiklian said there was "not much left" of the village of Balmoral, south-west of Sydney, due to an out-of-control, fast-moving Green Wattle Creek fire, which hit the town twice between Thursday and Saturday.

"We have still got an enormous amount of fire burning in the landscape," Shane Fitzsimmons, the head of state's Rural Fire Service (RFS), told reporters in Sydney on Sunday. 

"Fire behaviour continues to be very challenging for firefighters and those areas affected by fire." 

In Victoria, milder weather conditions helped firefighters to battle several fires on Sunday, but the blaze burning since November flared up on Saturday during an extreme heatwave after dry lightning strikes started the fire in several areas.

The bushfire season started two months earlier than in previous years, with severe drought in most of eastern Australia for the last two years exacerbating conditions.

So far, more than 800 homes have been destroyed in NSW and the bushfires have reached the outskirts of the state capital Sydney, Australia's most populated city.

The harbour city has also been choking on air pollution due to bushfires smoke, with authorities saying out of 48 days since November 1, 28 days had "hazardous" level of air quality.