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Police in Maryland said "a violent episode" had been avoided after they detained a man who described himself as "a joker" and allegedly threatened to shoot his colleagues.

The man, who police have not yet named, is said to have told an employer at Pitney Bowes in Prince George's County that he was "going to load my guns and blow everyone up".

Police said they found 25 guns and thousands of rounds of ammunition during an early-morning raid at the man's house in Crofton, Maryland. "We can't measure what was prevented here," said Prince George County police chief Mark Magaw.

"But what was going on over the last 36 hours was a significant incident in the county, and we think a violent episode was avoided."

Police said the man was in the process of being made redundant at Pitney Bowes when he allegedly made two separate, threatening calls to his boss.

Police were alerted to the threats on Wednesday, the day at least one of the calls was made. After a multi-agency planning operation that took 36 hours, officers raided the suspect's home at 3.20am Friday.

Among the weapons found on the property were semi-automatic rifles and pistols.

Police said the man had not resisted when taken into custody. He is undergoing a "mental evaluation" at a hospital in Maryland. "In light of the events in Aurora, it is important for the community to know that we take all threats seriously," Magaw said.

Pitney Bowes said in a statement that the suspect arrested was an employee of a subcontractor to Pitney Bowes. The company said that the man has not been on any Pitney Bowes property in more than four months.

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