A former prison guard trainee who recently moved to Florida from Indiana killed five people during a standoff at a small town bank before surrendering to a SWAT team that stormed the building, police said.

Investigators said Zephen Xaver, 21, called police from inside the SunTrust Bank branch on Wednesday to report that he had opened fire.

He barricaded himself inside and when negotiations failed, the SWAT team burst in, capturing Xaver and discovering the bodies, police said.

Investigators did not offer a possible motive, and a police spokesperson said he did not know if the attack began as a robbery. The victims were not immediately identified as families are still being notified.

"Today's been a tragic day in our community," Sebring Police Chief Karl Hoglund said during a news conference. "We've suffered significant loss at the hands of a senseless criminal doing a senseless crime."

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According to data from the Gun Violence Archive, a not-for-profit organisation that provides online public access to information about gun-related violence, the attack in Sebring is the nation's 19th mass shooting in 2019.

The Gun Violence Archive defines a mass shooting as any single event in which four or more people are shot or killed, not including the attacker.

An uneventful past

Public records and neighbours said Xaver had arrived in Sebring last fall with his mother, living in a non-descript pre-fabricated home about 6.5km from the bank. Public records and neighbours say he and his mother moved to Sebring in the fall from Plymouth, Indiana, a town south of Notre Dame University.

No one answered the door on Wednesday night after police finished searching the home.

John Larose, who lives next door, said Xaver kept to himself, but he could hear him playing and yelling at video games in the middle of the night.

Xaver briefly was an online student of Salt Lake City-based Stevens-Henager College. A spokesperson for the college, Sherrie Martin, confirmed that Xaver was enrolled from September 2018 until December, when he withdrew.

Florida Department of Corrections records show that Xaver was hired as a trainee prison guard at Avon Park Correctional Institution on November 2 and resigned January 9. No disciplinary issues were reported.

'Swift and exacting justice'

Governor Ron DeSantis was in the region for an infrastructure tour and travelled to Sebring after the shooting.

He said the Florida Department of Law Enforcement would assist Sebring police and the Highlands County sheriff's office.

"Obviously, this is an individual who needs to face very swift and exacting justice," DeSantis said of the suspect.

SunTrust Chairman and CEO Bill Rogers released a statement saying the bank was "working with officials and dedicating ourselves to fully addressing the needs of all the individuals and families involved". The bank's "entire team mourns this terrible loss" he said.