A thundering explosion rocked a Kansas grain elevator and shot a fireball so high it could be seen in neighboring Missouri, leaving three workers dead and three other people missing, authorities said Sunday.

Trey Cocking, city manager in the northeast Kansas town of Atchison, confirmed the deaths and said three others remain unaccounted for after Saturday night's blast at the Bartlett Grain Co. elevator, which shook homes and businesses all around. Authorities also reported injuries, but were still trying to get accurate information and notify families.

Cocking said authorities planned to bring in heavy equipment to dig through the rubble Sunday.

"Once we get light, we'll go from there," Cocking told The Associated Press as he left the site before dawn Sunday for a break after hours there. "From this point, they're going to have to do some excavation and bring in some crews."

The explosion could be seen and felt across Atchison, shaking homes and businesses up to four miles away. The cause was not immediately known, though grain elevator accidents can occur after grain dust becomes suspended in the air and turns explosive in the right conditions.

Bartlett Grain President Bill Fellows said in a statement that 11 workers were loading a train with corn when the explosion occurred about 7 p.m. Saturday. He said several of those 11 workers escaped injury, but that there were fatalities and some injuries.

Dennis McCulloch, spokesman for the University of Kansas Hospital in Kansas City, Kan., had said Saturday that two victims were in critical condition in the hospital's burn unit. It's not clear whether those victims are among those now said to be dead. He did not immediately return AP's messages early Sunday seeking updates.

Randy Burton, who works at a 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."

Across the nearby Missouri River, a dispatcher at the sheriff's department in Buchanan County, Mo., said the office received numerous calls from alarmed 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.

Fellows said Bartlett Grain workers remained at the elevator early Sunday and aiding authorities any way they could.

"The company's concern at this point is caring for those involved and their families," Fellows said. "We, of course, are in touch with all of the families of the Bartlett employees. We will share more information as it is discovered."

A news release from Atchison city officials said multiple injuries were reported, but that authorities were withholding details pending notification of families.

City officials said in the release that rescue operations "can be difficult because workers are often scattered throughout the facility, making them difficult to locate."

Their statement also gave no preliminary indication of the cause. But it noted the risks that working with grains can pose.

"Stored grain can generate toxic gases or dangerous molds. Milled grain can be explosive under certain conditions," the statement noted.

Units from several area police and firefighting agencies rushed to the site late Saturday, and fire crews pumped water onto the smoldering wreckage of the grain elevator for hours. Cocking said about 100 personnel joined in that work late Saturday night.

Access roads leading to the elevator were blocked by authorities.

Atchison has about 11,000 residents and is known as the birthplace of aviation pioneer Amelia Earhart.