The wave of destruction hit suddenly and catastrophically, swallowing up homes and twisting apart cars, and leaving behind a massive field of debris and countless families torn apart in a matter of moments.

Hundreds of rescue workers are spending a sixth day searching the aftermath of the landslide in Washington state, navigating treacherous conditions as officials cling to fading hopes that there may be survivors left in the carnage.

But the coming news is expected to be bleak. The death toll is expected to rise “substantially,” said Travis Hots, the Snohomish County District 21 fire chief.

“It’s going to be a very difficult day,” Hots said in a news conference Thursday morning.

The confirmed death toll had risen to 17 on Thursday night after the county revealed the grim news that workers had recovered an infant. Hots said Thursday that the toll was sure to go up. Searchers had already located several other bodies, but they hadn’t been recovered and cleared by the medical examiner’s office.

In addition, there are still 90 people reported missing as of Thursday night. While that number is significantly down from the 176 people authorities said had been reported missing earlier in the week, it still points to the scope of how many lives may have been lost, how many people are still waiting for word and how much is still unknown about the landslide’s true toll.

The landslide struck on a Saturday morning near the small town of Oso. It hit at the worst possible moment, authorities said, because on a weekday morning people may have been at work or school. Instead, people were home, contractors were coming to the area to do work and cars were passing through.

The slide area spans a square mile, with the debris field itself posing significant challenges to the workers trying to locate bodies. It may be as deep as 30 to 40 feet in  places, according to the Washington State Department of Natural Resources. And it’s a mass of mud, piles of wreckage and spilled septic material and gasoline, creating incredibly tricky conditions for people attempting to search.

“Our rescuers were sinking down to their thighs in the soft silt,” Bill Quistorf, the chief helicopter pilot for the Snohomish County Sheriff’s Office, said during a news conference Wednesday.

Some crews had been temporarily pulled from the slide area earlier this week due to concerns about additional slides, but there are no risks of that right now, said Steve Thomsen, the county’s public works director. “The slide’s stable right now,” he said.

More rain Thursday was expected to create additional challenges. As workers use their bare hands and shovels to dig through the wreckage, search dogs remain a key tool. It’s not a foolproof way to search, because they can pick up a scent that could be originating 50 feet away, Hots said Thursday, but it’s effective. If they think the dogs found something, they begin digging, bringing in machines if they are needed — and if they can be safely used.

“There’s a lot of areas out there we can’t get machinery in,” he said. “It’s so wet and mucky, it’s like a swamp.”

The search is taking an emotional toll on the rescue workers. During a media briefing Wednesday, searcher Randy Fay got choked up talking about the rescue of a young boy who made him think of his own grandchild.

“When a person is removed, things get kind of somber out there,” Hots said. “You see seasoned veterans in this business, they start to tear up.”

The list of names reported to be missing had reached 176 on Monday and remained that way for nearly two days before many people on that list were confirmed to be safe, according to John Pennington, the county’s emergency management director. However, there are still 90 people missing and an additional 35 names unaccounted for, he said.

“It’s definitively 90 people we can identify as unaccounted for or missing. It’s 35 we just don’t know,” he said.

Pennington said that he believes the list of missing people might drop again. But when asked during a news conference Wednesday if he’s worried that there are 90 bodies still in the debris, he replied, “Of course I am.”

No survivor has been located since Saturday, the day of the slide. But workers continue to press on with an effort focused on rescue as well as recovery, even while they acknowledge that the odds of finding a survivor have dwindled.

“We’re not changing gears, we’re not changing the pace of this,” Hots said. “We’re going to exhaust all options to try to find somebody alive. If we just find one more person that’s alive, that’s worth it.”

Related: Eight questions about landslides.

This post has been updated. Last update: 12:31 a.m.