Officials have had to bring a mobile morgue unit to help identify the remains of people killed in the wildfires that ravaged the island of Maui.

Around 1,300 people are still missing and as rescue workers and dogs comb through the ruins they have been told to expect to find many more corpses, especially in the historic town of Lahaina which was destroyed by the flames.

Even where the fires have retreated, authorities have warned that toxic byproducts may remain, including in drinking water, after the flames spewed poisonous fumes.

The US Federal Emergency Management Agency (FEMA) says it’s working closely with state, county and federal partners in the response efforts and to help survivors.

On the ground, there are more than 190 search and rescue team members and over 380 FEMA employees.

As rescue and clean-up efforts continue there is also a focus on how the fires started and spread so quickly.

Footage has emerged as key evidence pointing to fallen utility lines as the possible cause.

“I hear a pop coming from across the street,” said resident Shane True. “Soon as I hear the pop, all I heard is like electrical, like going on the ground there. I look, there’s a power line right there and shortly after, it was just arching away on the ground, landed right in dry grass, so sparks, and then there was a fire.”

Hawaiian Electric Co. faces criticism for not shutting off the power amid high wind warnings and keeping it on even as dozens of poles began to topple.

A class-action lawsuit has already been filed seeking to hold the company responsible for the deaths.

The suit cites the utility’s own documents showing it was aware that preemptive power shutoffs such as those used in California were an effective strategy to prevent wildfires but never adopted them.

Mikal Watts, one of the lawyers behind the lawsuit, told the AP this week that he was in Maui, interviewing witnesses and “collecting contemporaneously filmed videos.”

“There is credible evidence, captured on video, that at least one of the power line ignition sources occurred when trees fell into a Hawaiian Electric power line,” said Watts, who confirmed he was referring to Treu’s footage.

Hawaiian Electric declined to comment on the accusations in the lawsuit or whether it has ever shut down power before due to high winds.

But President and CEO Shelee Kimura noted at a news conference on Monday that many factors go into that decision, including the possible effect on people who rely on specialized medical equipment and firefighters who need power to pump water.

Experts say the early evidence suggests multiple blazes may have been ignited in and around Lahaina on 8 August and there were no recorded lightning strikes or other apparent natural causes for the fires.