Police in Delaware are being asked to explain how officers shot dead an armed man who was sitting in a wheel chair.

Wilmington police said in a news release that they encountered the man on Wednesday afternoon "armed with a handgun."

Authorities say a shooting occurred and the man died at the scene. The news release did not elaborate and police would not release any additional information when contacted by telephone, the Associated Press said.

According to a city spokeswoman, Police Chief Bobby Cummings went to the scene and met with neighbours and relatives.

Wilmington spokeswoman Alexandra Coppadge also said police told her the man had shot himself Wednesday before they arrived.

Delawareonline said Alexis Anthony identified the man as her cousin, Jeremy "Bam" McDowell, 28, and said he was shot by officers five times.

She said police officers on scene told her he was trying to commit suicide and refused to drop the weapon he was going to use. Ms Anthony, who lives on the corner of Tulip and South Scott streets, then heard five gunshots and ran outside.

"They couldn't [use a Taser on] him?" Ms Anthony asked. "Instead, they killed him instead. They could have knocked him out of his wheelchair."