The girl was hit by the bus at around 4.30pm on Tuesday in Råcksta in north-western Stockholm. She was taken to hospital by helicopter but later died from her injuries.
"I have just received the sad news that the girl passed away overnight. The family has been informed," police press spokesperson Per Fahlström told the TT news agency.
Police launched an investigation into the incident, but would not immediately say if they suspected any criminal offence. The bus was still being examined by a forensic team on Wednesday.
"The investigation will have to show what happened," said Fahlström.