A square near a tram station in the west of the city has been cordoned off by authorities, and emergency services are at the scene.
They have asked people to stay away to enable emergency workers to get through.
The gunman reportedly fled the scene by car. Police say they are investigating a “possible terrorist motive”.
Local media report the Dutch anti-terrorism co-ordinator has called a meeting. Prime Minister Mark Rutte said he was “deeply concerned”.
The shooting took place around the 24 Oktoberplein junction at about 10:45 local time (09:45 GMT). Three helicopters have been despatched.
Security services have reportedly told Utrecht’s University Medical Centre to open the dedicated emergency ward to help care for the injured.
“A man started shooting wildly,” one eyewitness told Dutch news site NU.nl.
Another witness told Dutch public broadcaster NOS he saw an injured woman with blood on her hands and clothes.
“I brought her into my car and helped her,” he said. “When the police arrived, she was unconscious.”
It is unknown how many were injured or how seriously they were hurt.
Utrecht’s transport authority said tram services in the city have all been cancelled.