Human remains have been found at the site of a massive fireworks warehouse explosion that detonated in Northern California earlier this week, and where seven people remained unaccounted for, officials said Friday.

Yolo County in a statement did not say how many human remains were found at the site of the explosion near Esparto, northwest of Sacramento, which caught fire and blew up on Tuesday.

Relatives of the seven missing people have expressed frustration with not knowing the fates of their loved ones.

Fire officials have said that the area was still burning and there were explosives at the site that required caution before recovery, and asked for patience.

“At this time, no positive identifications have been made,” Yolo County said in a statement.

Once identifications are made, next of kin will be notified before the names are publicly released, it said.

The cause of the fire and explosion remains under investigation, officials said.