(Reuters) – At least two workers were confirmed dead Saturday as rescuers searched the rubble of an Amazon.com Inc (AMZN.O) warehouse near St. Louis that collapsed when tornadoes and strong storms roared through the area, local authorities said.

Several people remained unaccounted for at the facility in Edwardsville, Illinois as first responders searched for those who might still be trapped, Police Chief Mike Fillback told reporters.

Amazon CEO Andy Jassy posted on Twitter that the company was “heartbroken over the loss” of its staff members in Edwardsville and would continue to work closely with the local authorities on the rescue efforts.

Relatives desperate for news about loved ones gathered outside the warehouse. One mother told a St Louis Fox news station that her son Clayton Cope, a 29-year-old maintenance worker, was dead. Police were yet to officially release names.

“You have concrete, and you have things hanging. It’s quite windy outside, so things are unstable, so they have to shore those things up so that they can be safe,” Fillback said. “Our first responders will continue to work this scene until everyone is accounted for.”

Fillback said about 50 workers were believed to be at the warehouse when it was hit by an extreme “weather-related event” about 8:30 p.m. Friday. A devastating swarm of tornadoes ripped through six U.S. states, leaving a trail of death and destruction at homes and businesses that stretched more than 200 miles.

At least 30 workers were transported by bus from the scene and others may have left on their own, Fillback said. He said it had been difficult to get an exact number of workers who might be unaccounted for because the warehouse did not have “a set staff.”

Drone footage from the scene showed rescue workers picking through a huge area of debris in the pre-dawn darkness.

Sarah Bierman, said she was very worried about her husband, who works at the warehouse.

“I talked to him about eight o’clock tonight, a little before I texted him, and he was returning to the warehouse to drop his van off,” she told a reporter.

“And I haven’t heard from him since, I just heard through the news and we live in Edwardsville; we lost power. So I decided to come down here to see what was going on, and I had no idea the building looked that bad. And I’m just; I’m worried sick,” she said.

Fillback said the fire department, with assistance from local construction companies, were trying to clear debris from the concrete and steel structure.

Reporting and writing by Nathan Layne, Radhika Anilkumar, Njuwa Maina, Caroline Stauffer and Leela de Kretser; Editing by Frances Kerry, Edmund Blair and Diane Craft

By Auther