The 32-year-old man was injured and arrested on suspicion of attempted murder, authorities said. Inside the stolen ambulance, police found an Uzi submachine gun, a shotgun and what they said were "large amounts" of narcotics.
"It is too early to say whether this is terror-related, but we are investigating broadly and fully," police said in a statement. Investigator Grete Lier Mettid said the suspect was known to have had ties to far-right groups.
Police did not identify the man by name. "It is, however, too early to say anything about the motive," Lier Mettid told a news conference in the Norwegian capital. Johan Fredriksen, a senior police officer, said the ambulance ran into a stroller carrying two seven-month old twins, though they were not believed to be seriously injured.
An elderly couple who dived under a parked car to avoid the ambulance escaped injury. Police shot at the tires to stop the ambulance and did not target the man, Fredriksen said. The vehicle stopped after being rammed by police.
A video posted by several Norwegian media showed how police officers pulled the man out of the ambulance through the side window because the front door had been damaged when it collided with obstacles, including a road sign.
The yellow-and-blue ambulance was stolen after authorities responded to a traffic accident on an Oslo traffic circle in which a car had turned over. The man left the scene on foot and pointed a weapon at police officers before stealing the ambulance.
A 25-year-old woman who was a passenger in the overturned car was later arrested. Both the man and the woman are known to the police, Lier Mettid told reporters. Anders Bayer, a spokesman for Oslo University Hospital, confirmed to Norwegian news agency NTB that the ambulance was stolen by an armed person. Three employees in the vehicle when it was stolen were unharmed, Bayer added.
The Aftenposten newspaper published a photo showing a man wearing green trousers lying next to the vehicle surrounded by police officers. Another photo in the daily showed a handcuffed man, flanked by police, walking toward an ambulance stretcher.
A witness told the newspaper that the ambulance was driving at high speed followed by a police car in pursuit. "I heard several shots," Omar Khatujev told Aftenposten.