North Yorkshire Police tweeted at just after 9pm that it was currently dealing with an ongoing incident on Ouse Bridge.
“The bridge is closed to all vehicles and pedestrians so please avoid the area if at all possible,” it said.
“Thank you for your help.”
York Rescue Boat tweeted that its lifeboat had been launched on service at just before 8pm.
The bridge was still closed by police at after 10pm, with several police, ambulance and fire service vehicles at the scene.