(CNN) -- A massive blast at a grain elevator in northeastern Kansas killed three people and left three others unaccounted for, authorities said Sunday.
Two people were hospitalized with burn injuries, said Dennis McCulloch, a spokesman for the University of Kansas Hospital.
The explosion occurred around 7 p.m. Saturday at Bartlett Grain Company in Atchison, Kansas, the city's fire department said.
People three miles away felt the force of the blast, city officials said in a statement.
Authorities were investigating the cause. Stored grain can generate toxic gases and cause explosions under certain conditions, the city's statement said.
"Rescue operations can be difficult because workers are often scattered throughout the facility, making them difficult to locate," the statement said.
A spokesman for Bartlett Grain could not be immediately reached for comment.
The company operates a total of 18 grain elevators in the central United States, CNN affiliate KSHB reported.
The U.S. Department of Labor's Occupational Safety and Health Administration has completed two accident investigations at Bartlett Grain locations in the past decade, the CNN affiliate said.
In 2004, an employee fell to his death while working at the company's location in Kansas City, Missouri, according to KSHB. And in 2004, an employee fell off an elevated work platform at a grain elevator in St. Joseph, Missouri. As a result of that inspection, OSHA cited Bartlett Grain with three serious violations, and the company was fined $5,000 for each penalty, KSHB said.