SYDNEY: Australia's most populous state declared its second emergency in as many months on Thursday as extreme heat and strong winds stoked scores of uncontrolled bushfires, some on Sydney's doorstep.

In the same week the continent recorded its hottest day on record, thick smoke blanketed the harbour city, shrouded the Opera House and brought many outdoor activities to a halt.

The state of emergency declaration gave firefighters broad powers to control government resources, force evacuations, close roads and shut down utilities across New South Wales, where 100 wildfires are burning.

With more than half of those fires uncontrolled and temperatures forecast to hit 45 degrees Celsius (113°F) in some areas, officials warned residents to be on high alert.

"The biggest concern over the next few days is the unpredictability, with extreme wind conditions, extremely hot temperatures," NSW Premier Gladys Berejiklian told reporters in Sydney.

Days out from Christmas, a time when many Australians head to the coast for the holidays, Berejiklian warned people to reconsider travel plans.

"Please do your research before you embark anywhere across the state," she said. "Please make sure you are prepared to change your plans should circumstances change."

Australia has been battling wildfires across much of its east coast for weeks, leaving six people dead, more than 680 homes destroyed and nearly 3 million acres (1.2 million hectares) of bushland burnt.

Prime Minister Scott Morrison has weathered a storm of criticism on social media in recent days for going on an overseas holiday during the emergency, adding to criticism that his government is failing to deliver adequate climate change policies.

As the media reported Morrison was in Hawaii with his family to enjoy a break, about 500 protestors gathered outside his official Sydney residence to demand urgent action on climate change. Morrison's office refused to confirm his whereabouts.

One protestor carried a sign reading, "ScoMo, where the bloody hell are you?" referencing the leader's nickname and a decade-old international advertisement for Tourism Australia that was banned in several countries because the language was deemed offensive.

Some 1,700 firefighters have been deployed across NSW, but officials warned that was still not enough to cover every potential danger and urged people in high risk areas to evacuate while it was still safe to do so.

"There are simply not enough fire trucks for every house. If you call for help, you may not get it," the Rural Fire Service said in a statement. "Do not expect a fire truck. Do not expect a knock on the door. Do not expect a phone call."

The current state of emergency will last for seven days, while a total fire ban that has been in place since Tuesday will remain until midnight on Saturday.

SMOKY SYDNEY

Three major fires were burning around Sydney, which is home to more than 5 million people. One megafire in the Kanangra Boyd National Park to the city's southwest had crept to the very outskirts of Campbelltown, a suburb of 157,000 people.

Sydney is ringed by large areas of bushland, much of which remains tinder dry following the driest Spring on record.

Many commuters have donned breathing masks in recent weeks as air quality has plunged to hazardous levels not previously seen in the city.

NSW Ambulance Commissioner Dominic Morgan said the service had experienced a 10% surge in call-outs for patients suffering respiratory conditions over the past week and urged susceptible people to remain indoors and keep their medication close.

The heightened fire danger in NSW comes as Australia is in the grip of a nationwide heat wave.

The country recorded its highest average maximum temperature of 40.9C (105.6F) on Tuesday, and Bureau of Meteorology data shows that record was likely to be exceeded again this week.

The extreme conditions have been exacerbated by a warming climate, which is triggering large-scale protests in a country that has been committed to exploiting its vast coal reserves.

Australia's low-lying Pacific neighbours have been particularly critical of the coal-rich nation's climate policies following modest progress at the U.N. climate talks in Madrid.

"It was particularly disappointing to see our Pacific cousins in Australia actively standing in the way of progress at a time when we have been watching in horror as their own country is ablaze," Marshall Islands president Hilda Heine said in a statement on Wednesday.