The head of the Maui Emergency Management Agency resigned his post on Thursday in the wake of significant criticism for his agency's response to the Lahaina fire, which has claimed the lives of at least 111 people — the deadliest U.S. wildfire in more than a century.

Maui County officials said in a news release that MEMA Administrator Herman Andaya had resigned "effective immediately" due to "health reasons."

"Given the gravity of the crisis we are facing, my team and I will be placing someone in this key position as quickly as possible and I look forward to making that announcement soon," Maui Mayor Richard Bissen said in a statement.

When the Maui wildfires broke out Aug. 8, residents said they were not evacuated and none of the island's warning sirens sounded for evacuation.

When asked Wednesday by reporters if he regretted not activating the sirens, Andaya responded, "I do not."

"The public is trained to seek higher ground in the event that the sirens are sounded," Andaya said, noting that the sirens are generally used to warn of tsunamis or approaching storms.

"Had we sounded the sirens that night, we were afraid that people would have gone mauka (mountainside), and if that was the case, they would have gone into the fire," Andaya said. "So that is the reason why, it is our protocol, to use WEA [Wireless Emergency Alerts] and EAS [the Emergency Alert System]."

WEAs are text alerts sent to cell phones and the EAS uses television and radio, Andaya explained.

Hawaii's official government website lists "wildfires" as one of the hazards the siren alert system can be used for. However, with power knocked out in the area and no television or radio, residents reported receiving no text alerts or television or radio notifications. 

"In a wildland fire incident, the (siren) system has not been used, either in Maui or in other jurisdictions around the state," Andaya said.

CBS News learned that Andaya had no background in disaster response. Local news site Maui Now reported in 2017 that he was hired over 40 other qualified applicants.   

Andaya countered Wednesday that the claim "that I'm not qualified, I think, is incorrect."

He said that prior to taking the reins of the emergency agency, he served as deputy director of the state Department of Housing and Human Concerns, and spent 11 years as the Maui County mayor's chief of staff.

During that time, Andaya said, he often reported to "emergency operations" officials and went through "numerous trainings."

The cause of the wildfires remains under investigation. The Hawaii attorney general's office has also launched an investigation into the local government's response leading up to and after the fires broke out.

• How to help those affected by the Maui wildfires

Meanwhile, the search for victims intensified Thursday, with federal personnel -- using cadaver dogs now -- having canvassed some 58% of the burn area. FEMA spokesperson Adam Weintraub told reporters Wednesday that the number of people unaccounted for was estimated to be between 1,100 and 1,300. 

Hawaii Gov. Josh Green said in a video posted to social media Thursday afternoon that 41 cadaver dogs have now been flown in from the mainland U.S. to take part in combing the debris area.

There are nearly 500 FEMA personnel on the ground in Maui, along with 270 Red Cross workers, nearly 400 Hawaii National Guard members and close to 200 U.S. Army reservists. 

The Lahaina wildfire is one of four that broke out on Maui on Aug. 8, scorching a combined 5.7 square miles. Three of the four fires are still burning.

Maui County officials announced Thursday that two of those fires — which had been previously referred to as the single blaze — the Upcountry/Kula fire, were actually determined to be two fires with "distinct origins." Moving forward, they will be reported separately as the Olinda and Kula fires, officials said.

The two fires broke out on the eastern side of the island and have destroyed 19 homes.

The Olinda Fire has scorched 1.69 square miles and was 85% contained, while the Kula Fire has burned about one-third of a square mile and was 80% contained, officials said.

Firefighters battling those two blazes on the ground and in the air were still dealing with "hot spots in gulches, forests and other hard-to-reach places," officials said.

Meanwhile, the Lahaina fire, which has burned 3.39 square miles, was 90% contained Thursday, officials reported, with "no active threats at this time." The Lahaina fire has damaged or destroyed at least 2,200 structures, according to estimates. 

Six of the victims have so far been publicly identified. All were Lahaina residents. They are:

Robert Dyckman, 74
Buddy Jantoc, 79
Melva Benjamin, 71
Virginia Dofa, 90
Alfredo Galinato, 79
Donna Gomes, 71

In:
• Hawaii Wildfires