Firefighters in the Australian state of Victoria are trying to contain over a dozen fires which are threatening towns north-east of Melbourne.
Large areas of south-eastern Australia are swathed in smoke as some of the worst bush fires for nearly 70 years threaten mountain and country towns.
More than 2,000 firefighters are battling blazes which have destroyed more than 140,000 hectares (346,000 acres) of bush.
The fires in the state of Victoria, mostly in eastern alpine areas, have burned at least 180,000 hectares (445,000 acres) of drought-hit land.
At least six towns are under threat. Some risk being cut off for days.
There are fears that the blazes could merge into one "super fire".
Officials fear that high temperatures and strong winds forecast over the weekend could further fan the flames.
Bush fires are common in Australia's hot summer months, but this year's are being described as exceptional.
There is also concern that the fires could merge, potentially creating a blaze covering hundreds of thousands of hectares.
People in Victoria are recalling the state's "Black Friday" in 1939, when 71 people died in fires.
'Very scary'
It's the worst drought on record for Victoria, which means all the forest and grassland is extremely dry Rachaele MayVictoria environment spokeswoman
Residents have been told to decide now whether to evacuate or stay and defend their homes.
No-one has been killed in the latest emergency, but firefighters say expected rising winds and high summer temperatures mean extreme danger through the weekend.
"If you are not able to look after yourself, leave early. Do not leave late," a local fire officer, Russell Rees, told reporters in Melbourne.
It is feared some of the fires, mostly sparked by lightning strikes, could burn for months.
"The evidence is very clear and plain - late evacuation is deadly," he said.
The Australian army has been mobilised to back up local firefighters, who are also being helped by crews from beyond Victoria, as well as a specialist team from New Zealand.
The main area of concern is about 200km (120miles) north-east of Melbourne. Authorities said the communities at risk included Kevington, Mount Buller and Cheshunt.
The state government's environment spokeswoman, Rachaele May, said it was a "significant possibility" that all of the fires would eventually merge into one larger fire.
Mansfield and Wangaratta were at risk of being cut off by the fires, officials said.
"It's the worst drought on record for Victoria, which means all the forest and grassland is extremely dry," she told the Australian Broadcasting Corporation.
The firefighters are being backed up by dozens of aircraft, water tankers and bulldozers, although thick smoke had grounded the aircraft.
Flight delays
More firefighters - including some from New Zealand - are expected to arrive over the weekend.
Thick smoke has grounded aircraft used in operations to dump water on the flames, while smoke drifting hundreds of kilometres has blanketed the state capital, Melbourne, cutting visibility and disrupting passenger flights.
Bush fires are an annual problem in Australia, as hot weather, low humidity and strong winds combine to create tinderbox conditions.
Australia's largest airline, Qantas, reported flight delays of up to an hour from Melbourne.
Prime Minister John Howard told Southern Cross Broadcasting radio: "It's very, very scary stuff and the terrible combination of circumstances - high temperature, low humidity, all of those things - are very bad indeed".
A flight from Los Angles was diverted to Sydney, while a domestic flight from Sydney was diverted to the national capital, Canberra, to refuel.
Nine people died in fires on South Australia state's Eyre Peninsula in January 2005.
In 2003, more than 500 houses were destroyed and four people killed when a huge fire tore through the capital, Canberra.
Have you been affected by fires in Victoria? Send details of your experiences using the form below.
Have you been affected by fires in Victoria? Send details of your experiences using the form below.
