Image caption Firefighters paid their respects at a makeshift memorial in Prescott, the hometown of the squad who died in the wildfire

Nearly 600 firefighters are continuing to tame a blaze in central Arizona that killed 19 of their colleagues.

The fire, which has so far razed 13 sq miles (33 sq km), was at least 45% contained, authorities said..

Officials added they could not rule out the possibility some residents who refused to evacuate had also perished in the blaze.

The deadliest US wildfire in 80 years, it was ignited by lightning in forest around the town of Yarnell.

At least 129 homes have been destroyed by the blaze, which was fuelled by 40mph winds and dry conditions.

This fire moved approximately four miles in 20 minutes John Russell, Sheriff Chief Deputy

Officials on Thursday said gusts and thunderstorms also remained a threat.

Authorities said they hoped to allow Yarnell residents to return to their homes this weekend, the AP news agency reports.

Meanwhile, an initial autopsy report on the firefighters found the men had died from accidental "fire-related injuries", including burns and inhalation problems.

In the town of Prescott, the nearby hometown of the fallen squad, families of the dead men and their colleagues from across the state are expected to attend an Independence Day fireworks display.

Fire officials say they will take precautions to ensure the pyrotechnics do not spark another blaze in the tinderbox conditions.

Arizona Governor Jan Brewer has ordered state flags to be flown at half-mast for 19 days to honour each firefighter lost.

Only one member of the unit survived, a lookout on higher ground who was about a mile away from the others.

Hundreds of residents were evacuated, but some refused to leave. Authorities fear finding more bodies during the clearing-up operation.

"This fire moved approximately four miles in 20 minutes," Yavapai County Sheriff Chief Deputy John Russell told Reuters news agency.

"We had already started evacuating everyone... and we experienced people who were not going to leave."

Investigators are trying to determine how the members of the elite Granite Mountain Hotshots became trapped by the flames.

The inquiry team, which includes forest managers and safety experts, is expected to release a preliminary report within days.

Sunday's tragedy marked the greatest loss of life from a US wildland blaze since at least 25 men died in 1933 battling the Griffith Park fire in Los Angeles.

How wildfires spread

A fire needs fuel, oxygen and heat to burn. The fire threatening the town of Yarnell was started by lightning and spread rapidly in the very hot, dry conditions, fanned by strong winds

The fastest-moving and most dangerous part of the fire is known as the "head". Areas ahead of the fire are warmed as it approaches and flying embers blown by the wind spark spot fires, which cause it to leap further ahead

Some vegetation or fuel will burn quicker than others and this creates "fingers" of flame which, in turn, create pockets of land surrounded by fire, making it harder to tackle