PM Scott Morrison had to cut short a visit to one fire-hit town after being heckled by angry residents.

He was accused of doing little to help Cobargo in New South Wales (NSW), where two people died this week and many others lost their homes.

Locals told Mr Morrison he wasn't welcome, and wouldn't get their votes.

Thousands of people are fleeing a vast "tourist leave zone" in NSW, with supplies running low in some cut-off towns. It's been called "the largest relocation out of the region ever".

Meanwhile troops are preparing to evacuate some of the 4,000 people trapped by fires in neighbouring Victoria state.

A naval vessel has arrived off the coastal town of Mallacoota, near the NSW border.

Victoria Premier Daniel Andrews said the ship would take up to 800 people early on Friday. He said it could do "multiple trips".

Defence Minister Linda Reynolds tweeted that the HMAS Choules was in position.

Since September, bushfires have killed 18 people and destroyed more than 1,200 homes across NSW and Victoria.

At least 17 people are missing after fires this week alone.

'What could be a horrible day'

The state of emergency in NSW will kick in at 08:00 on Friday (21:00 GMT on Thursday) and last for seven days.

It will allow local authorities to carry out forced evacuations, road closures "and anything else we need to do as a state to keep our residents and to keep property safe", NSW Premier Gladys Berejiklian said on Thursday.

"We don't take these decisions lightly but we also want to make sure we're taking every single precaution to be prepared for what could be a horrible day on Saturday."

High temperatures and strong winds are forecast for the weekend, leading to "widespread extreme fire danger".

The state government has warned that conditions are likely to be "at least as bad" as New Year's Eve, when hundreds of homes were destroyed.

Earlier, fire officials told holidaymakers to urgently leave a 260km (160-mile) stretch of NSW coast before Saturday.

Long lines of cars have clogged highways leading back towards Sydney and Canberra.

Local media reported hour-long queues for petrol in the town of Batemans Bay, while fuel was being trucked in to the region as supplies dwindled.

Many roads remained closed due to continuing fires and other dangers, such as unstable or fallen trees.

Workers were clearing roads, restoring power, and conducting "backburning" operations to thin out bushland near fire fronts.

NSW Transport Minister Andrew Constance urged people to drive slowly amid thick smoke.

This week's fires have destroyed at least 381 homes in NSW and 43 in Victoria, but officials say that number will grow.

The seven deaths in NSW include:

• Two people found in separate cars on Wednesday morning
• A father and son who stayed behind to defend their home and farm equipment
• A 28-year-old volunteer firefighter who was killed when wind flipped his fire engine

Family members of Mick Roberts, a 67-year-old Victorian missing since Monday, confirmed that he had been found dead in his home in Buchan, East Gippsland.
"Very sad day for us to (start) the year but we're a bloody tight family and we will never forget our mate and my beautiful Uncle Mick," his niece Leah Parson said on Facebook.

Mr Andrews said there were "significant fears" for 17 people unaccounted for in his state.


Police brought water, food and medical supplies into Mallacoota by boat

Fire services in Victoria and NSW warned they had been unable to reach some people in remote areas.

In the capital Canberra - an administrative region surrounded by NSW - bushfire smoke meant air quality there was rated worse than any major global city on Thursday, according to Swiss-based group AirVisual.

An elderly woman died after being exposed to the smoke as she exited a plane at Canberra airport, local reports say. Australia Post has suspended deliveries in the city "until further notice"