Australian Prime Minister Scott Morrison has faced criticism for holidaying in Hawaii while thousands of firefighters have battled bushfires. — AFP/VNA Photo

SYDNEY — Australian Prime Minister Scott Morrison cut short a Hawaii holiday on Friday following a barrage of criticism for vacationing while his country endured an unprecedented bushfire crisis.

Morrison expressed regret for the trip, with his announcement coming shortly after two volunteer firefighters were killed and a record heatwave this week exacerbated dozens of out-of-control blazes.

Pressure had been piling up on Morrison over his vacation this week, as thousands of exhausted volunteer firefighters battled blazes across the country and millions of people in Sydney choked on toxic smoke.

"I deeply regret any offence caused to any of the many Australians affected by the terrible bushfires by my taking leave with family at this time," Morrison said in a statement Friday.

He added he would be returning to Australia as soon as possible "given the most recent tragic events", referring to the deaths of the two firefighters.

Geoffrey Keating, 32, and Andrew O'Dwyer, 36 died when a tree damaged their truck on Thursday as they battled out-of-control blazes south of Sydney.

Three other firefighters in the vehicle survived with minor injuries.

'Huge loss'

New South Wales fire commissioner Shane Fitzsimmons said firefighters everywhere were grieving the "huge loss" of the two men who were caught in "the worst imaginable set of circumstances".

"(They) simply went out, doing a remarkable job, like all their colleagues, and like they have done year-in, year-out, and to not be coming home after their shift is a tremendous grief," he said.

The fire that they were battling remained out-of-control Friday morning and conditions were due to worsen on Saturday, leaving no time for their colleagues to grieve as conditions.

More than 100 fires are burning in New South Wales, the most populous state in Australia with Sydney at its capital.

A state of emergency was declared in New South Wales on Thursday because of the "catastrophic" conditions.

Aside from New South Wales, more than 70 fires are raging across Queensland state to the north. Bushfires are also burning in Western Australia and South Australia.

At least three million hectares of land has been torched across Australia in recent months, with eight people killed and more than 800 homes destroyed.

Australia endures bushfires every year but they began particularly early this season, lasted longer and have been far more intense.

Scientists have attributed this in part to global warming, although

Morrison's conservative government has been reluctant to link the fires with climate change.

A series of record temperatures this week has further raised the alarm about global warming, as well as worsened the bushfire crisis.

Australia endured a record national maximum temperature of 41.9 degrees Celsius on Wednesday.

This was a full degree higher than the previous record set just one day earlier.

Until this week, the record high had been 40.3 C in January 2013.

In some parts of Australia the temperature neared 50 C, and the heatwave was expected to continue into the weekend. — AFP