A young man fatally shot by Swedish police while carrying a toy gun in Stockholm had Down's syndrome and a form of autism, local media report.

Officers opened fire on Eric Torell, 20, in response to what they described as a "threatening situation" in the early hours of Thursday morning.

He was reported missing after leaving home hours earlier, his family said.

Eric's mother, Katarina Söderberg, said the toy was a gift and she described her son as "the world's kindest man".

Ms Söderberg told Swedish news outlet Expressen that Eric was severely disabled and struggled with his speech, only ever really using the word "mum".

She described the plastic toy he was carrying at the time of the shooting as "like a submachine gun".

"It's impossible to understand. He wouldn't hurt a fly," Ms Söderberg said.

The incident occurred at about 04:00 local time in the Vasastan district of the Swedish capital, Stockholm, after police responded to reports of a man in possession of a gun.

Three officers reportedly arrived at the scene and approached Eric before ordering him to discard what they believed to be a dangerous weapon. He was then shot after failing to comply and acting "threateningly", police said.

Eric was taken to hospital but was later confirmed dead from his injuries.

Ms Söderberg said her son had left home a number of times previously but had always been found or returned.

An investigation into possible police misconduct is now under way, Expressen reported.