A swarm of bees estimated to number between 30,000 to 60,000 attacked people in a Walmart parking lot in Oklahoma City. Three people were hospitalized as a result of the incident.

Emergency Medical Services Authority (EMSA) spokesperson Lara O'Leary said that two of those who were taken to the hospital were transported in serious condition after they were stung on Saturday morning after the insects escaped from three hives.

The incident started about 10:30 a.m. when a person who sells beehives met a buyer in the parking lot of the Walmart Neighborhood Market off Sooner Road and the bees escaped.

EMSA field operations supervisor Colin Roy explained that the movement of the bees from one car to another disturbed the bees and likely caused them to escape. Three hives were being sold, and each of these contains more than 10,000 bees.

"The bee keeper that we spoke to on the scene said that each hive can have up to 22,000 bees and at the time there were three hives she counted and she said they were about half full at that time," Roy said, explaining that there were at least 30,000 bees.

He said that attacks of large bee swarms such as this are not common since most bee attacks only involve between one and two bees. An attack by a swarm, though, poses more concern because bees may sting the same person. The swelling from multiple stings may eventually affect the person's eyesight and breathing.

Bee stings in people who have insect sting allergy may also cause a potentially deadly anaphylactic reaction. In May, an attack of aggressive bees in northern California left two dogs dead.

Several people in the area were stung. When honeybees sting, they release pheromones that also prompt other bees nearby to attack.

Oklahoma City Fire Battalion Chief Benny Fulkerson said that beekeepers were called to gather the bees.

One of the firefighters who responded was also stung but did not need medical attention, Fulkerson said. The fire crews sprayed water in the area to distract the bees and prevent them from attacking people nearby.

Walmart was evacuated for several hours because of the danger posed by the swarm of bees. Beekeepers and responders worked together to keep people safe.

EMSA officials said that they have removed the truck that was used to bring in the bees because it could attract the insects back to the area.