? A hunt was on for survivors of an explosion at a northeast Kansas grain elevator injured at least two people Saturday, shaking the ground for miles around and sending a fireball high into the night sky that was visible across the river in Missouri.

Authorities said the blast shook homes and businesses up to 4 miles away.

The two injured victims were in critical condition in the burn unit at Kansas University Hospital in Kansas City, Kan., about 50 miles south of the blast site at the Bartlett Grain Co. elevator in Atchison, Kan., hospital spokesman Dennis McCulloch said. It was not immediately clear how many people may have been in or around the elevator at the time of the explosion.

Atchison City Manager Trey Cocking said search and rescue efforts were under way to try to find “several” people who’d not been accounted for, but he couldn’t say exactly how many or whether they were workers or others.

A news release from Atchison city officials said multiple injuries were reported, but that authorities were withholding details pending notification of families. A spokeswoman for Atchison Hospital, TC Roberts, said the hospital had not treated any patients from the explosion and didn’t expect to receive any.

The cause of the explosion was not immediately known, though grain elevator mishaps often occur after grain dust becomes suspended in the air and turns explosive in the right conditions. In its news release, the city said rescue operations “can be difficult because workers are often scattered throughout the facility, making them difficult to locate.”

Several area police and firefighting agencies were on the scene late Saturday, and fire crews were seen pumping water onto the wreckage well into the night. The elevator’s roof appeared to have been blown off, with another large piece of the structure hanging off the side, the St. Joseph, Mo., News-Press reported. Access roads leading to the elevator were blocked by authorities as the search-and-rescue effort was under way.

The explosion at about 7 p.m. could be seen and felt across Atchison, a town of about 11,000 people known as the birthplace of aviation pioneer Amelia Earhart.

Across the river in Buchanan County, Mo., a sheriff’s dispatcher said their office took numerous calls from residents saying they could hear the explosion deep into the county. Residents across the area said a fireball from the explosion could be seen well away from the site.

Randy Burton, an employee at the Quick Stop East convenience store in Atchison about two miles from the elevator, said the explosion “shook our whole building.”

“All I saw was a flash and then the building shook really good,” Burton said. “Some things fell off our shelves.”