"We believe these three incidents are all linked and we have a man in custody.
"This investigation is at its early stages and a team of detectives is working to establish exactly what has happened.
"We ask the public to be patient while inquiries continue. At this time, a number of roads in the city will remain closed as this investigation progresses."
Earlier, Nottinghamshire Police said: A man has been arrested on suspicion of murder after three people were killed in the city.
"Police were called to Ilkeston Road just after 4am where two people were found dead in the street.
"Officers were then called to another incident in Milton Street where a van had attempted to run over three people. They are currently being treated in hospital.
"A man has also been found dead in Magdala Road," they said in a statement.
"Police have arrested a 31-year-old man on suspicion of murder and he remains in police custody."
