LONDON — London firefighters traumatized by the devastation they witnessed in a high-rise apartment blaze that killed at least 12 people worked today to make the building safe so they could continue the search for more victims.

Entire families are missing, and the death toll is certain to rise after flames tore through the 120-unit Grenfell Tower where up to 600 lived in the early hours Wednesday. Fire Commissioner Dany Cotton said it would be a miracle if anyone were to be found alive.

It is unsafe for firefighters to go to all parts of the 24-story tower, so the fire department is working with structural engineers to shore up the building so they can complete a “finger-tip search” of the entire structure, Cotton said.

“I spoke to one of my officers who was very near when someone came out the window, and he was in tears and he is a professional fire officer,” Cotton told Sky News. “We like to think of ourselves as ‘roughty, toughty’ and heroes — they are heroes — but they have feelings, and people were absolutely devastated by yesterday’s events.”

More than 200 firefighters worked through the night, and parts of the building were still unsafe. The blaze in west London’s working class, multi-ethnic neighborhood of North Kensington district injured 74, 18 of them critically, and left an unknown number missing.

The cause of the fire is under investigation, and authorities have refused to speculate on what could have started the blaze. But the focus has turned to renovations completed last year that added decorative touches to the building.