Image copyright Botham Shem Jean/Facebook Image caption Botham Shem Jean was reportedly a native of the Caribbean nation of St Lucia

A police officer in the US state of Texas has shot and killed a man in a flat after mistakenly thinking she was in her own unit, police say.

The unnamed Dallas officer entered the apartment after her shift on Thursday night and confronted the victim, 26-year-old Botham Shem Jean.

Jean was treated on scene and taken to hospital, where he later died.

The officer has been placed on leave while the police and District Attorney's Office investigate.

Local media report Jean was a native of St Lucia.

Police Chief Renee Hall said at a news conference on Friday that the incident appears to be a "very unique situation".

"We have ceased handling it under our normal officer involved shooting protocol," Chief Hall said. "Right now there are more questions than answers."

Police say they have taken a blood sample to test for drugs and alcohol and are obtaining a warrant for the officer's arrest.

The Dallas Police have also invited the Texas Rangers to conduct an independent investigation.

Image copyright Dallas PD/Twitter Image caption A police officer in Dallas, Texas shot a man after walking into the wrong apartment

The shooting occurred at an upscale apartment complex just one block from the police department, south of downtown Dallas.

According to a police statement, the officer walked into the unit she believed belonged to her and saw Jean inside.

Authorities did not provide further details about how the altercation unfolded, but the officer eventually fired her gun and hit Jean.

The off-duty officer, who was still in uniform and not injured, called police to report the shooting.

The officers who responded four minutes later provided first aid at the scene before Jean was taken to Baylor University Medical Center and pronounced dead.

In a news conference on Friday morning, Dallas Police Sgt Warren Mitchell said they had not yet interviewed the officer involved.

Sgt Mitchell did not comment on whether the officer had mistaken Jean as an intruder when she shot him.

"We still have a lot to do in this investigation," he told reporters, the Dallas Morning News reported.

Police have not spoken to any other individuals at this time and did not say that there were any witnesses.

The Dallas Police Department and the District Attorney's Office are conducting a joint investigation.

Jean had been interning at a company in Dallas, according to NBC News.

His mother, Allie Jean, told NBC the family was shocked to hear of his death.

"Somebody has to be crazy not to realise that they walked into the wrong apartment. He's a bachelor. Things are different inside," she said.

"And if you try your key and it doesn't work, that should make you realise you're at the wrong apartment."