Death toll from London high-rise fire climbs to 30; victims may never be identified, police say

— -- The death toll from a fire that engulfed a residential high-rise building in London this week has climbed to 30 as rescue workers continue to search for survivors, police said, adding that the blaze did not appear to have been deliberately started.

The flames have now been extinguished but the number of dead is expected to rise and the likelihood of finding survivors at this point is slim, Stuart Cundy, commander of the Metropolitan Police Service in London, told reporters at a news conference Thursday afternoon.

The bodies of 12 people have been recovered and are at a mortuary, including one person who died after being taken to a hospital. The other 18 bodies remain inside the scorched building, police said.

Cundy noted that the ongoing operation to recover and identify all victims is a complex process, and some may never be identified.

"The conditions inside Grenfell Tower mean that the search-and-recovery operation to find and recover the victims is extremely challenging. The upper floors of the block are particularly hazardous due to the damage caused by the fire. The sad reality is that this work will take some time, stretching into many, many weeks," the police commander said. "Sadly, the nature of injuries caused by such an intense fire will mean the identification process will take some time. But it would also be deeply distressing for families for us to release wrong information."

In addition to those killed, the blaze injured at least 74 people. As of Thursday afternoon, 24 remain hospitalized, with 12 in critical condition, he said.

The Metropolitan Police Service, which is leading the ongoing investigation, believes it has identified the origin of the fire, which so far does not appear to have been intentional, Cundy said. The exact cause of the fire is still unknown.

Investigators believe the fire started at around 1 a.m. local time Wednesday on the fourth floor of the 24-story Grenfell Tower in North Kensington, an area of West London. The London Fire Brigade dispatched more than 200 firefighters, at least 40 fire engines and about 20 ambulance crews in an effort to battle the inferno.

Fire officials said it took nearly two hours to gain control of the conflagration.

"This is an unprecedented incident," London Fire Commissioner Dany Cotton told reporters Wednesday night. "In my 29 years of being a firefighter, I have never, ever seen anything of this scale."

The fire has left the building almost completely charred, and there were concerns about the tower's structural integrity, as it appeared to lean slightly to one side.

It's unclear exactly how many residents were inside the building at the time. But the tower, built in 1974, contained 120 apartments, according to its management company, the Kensington and Chelsea Tenant Management Organization.

U.K. Prime Minister Theresa May, who visited the still smoldering wreckage Thursday morning, promised a "proper investigation."

London Mayor Sadiq Khan said Wednesday he was "truly devastated" and warned that the death toll could increase.

ABC News' Karma Allen, David Caplan, Joshua Hoyos and Joseph Simonetti contributed to this report.