(CNN) - A gunman boarded a school bus in Alabama, took a 6-year-old boy hostage and killed the driver who tried to save him, police said Wednesday.
The incident occurred Tuesday and continued into Wednesday morning, with authorities still desperately trying to free the young child, who was being held by the gunman in an underground bunker.
"We will continue to work diligently through the night in an effort to bring closure to this incident as quickly as possible," the Dale County Sheriff's Department said late Tuesday.
Authorities identified the slain bus driver as 66-year-old Charles Albert Poland Jr.
Late in the evening Tuesday, the shooter had the child in some sort of underground bunker or storm shelter, and authorities were communicating with him through a PVC pipe, CNN affiliate WSFA reported.
Adding to the tension was the fact that the child needs medication that has to be taken daily, CNN affiliate WDHN reported.
Overnight, authorities were able to send the child's medication down the pipe into the bunker and also determine that the boy had not been physically harmed, WDHN reported.
The incident started at about 3:40 p.m. (4:40 p.m. ET) near a church in Midland City, Alabama, in the southeastern corner of the state. Authorities have since expanded an evacuation area in an effort to protect nearby residents.
Michael Senn, a local pastor, told WSFA that he spoke to several students who had been on the bus.
He said a girl described the shooter getting aboard.
"He told most of them to get off the bus," Senn related. "And then he grabbed a little boy and shot the bus driver four times." The driver's body was removed from the bus early Wednesday, WDHN reported.
Mike Creel, the suspect's neighbor, said he also talked to some of the children who escaped the bus. It was a terrifying scene, Creel told the affiliate.
The suspect initially demanded two children, Creel told WSFA.
"The one child he got ahold of actually fainted," said Creel. "That was the reason he was able to grab him. And now he is hidden in his homemade bomb shelter."
Creel said the suspect had been living in the area for about two years and began building the shelter right when he moved in.
Authorities have not released the name of the suspected gunman.
Early in the morning, local authorities allowed the FBI to take the lead in the hostage situation, WDHN reported.