The incident is taking place outside The Lair near the city centre.
One witness reported hearing “gunshots” and another a “few bangs” though this hasn’t been confirmed by police.
A pub employee said the venue had been called by police, told to stay away from the windows and close their shutters as a precaution.
Speaking to Hull Live one man said: “Nobody knows what’s going on.
"The police rang the landlord and asked him to tell us to get away from the windows. We are allowed round the back, but not the front."
One women claimed her mother, who lives in a tower block overlooking the scene, heard multiple “gunshots”.
Another women living nearby reported “a few bangs” before armed police arrived at the scene.
On Twitter Humberside Police said: “Anlaby Road in Hull is currently closed between Ferensway and Park Street as police are dealing with an ongoing incident.
“We ask people to please avoid the area to assist us in bringing the incident to a safe conclusion.”
Roads around Cambridge Street have been blocked off by the police.
Disruption is also affecting nearby St Lukes Street and Pease Street.
Speaking to Hull Live from Paragon Square a local commented: “They’re strictly not allowing people down there.
“It’s very quiet but cars are being turned away and they were blocking off nearby streets.”
Pictures from the scene show the road being blocked by police vehicles.
Commenting on Twitter one local said: “I hope everyone is okay at the incident down Anlaby Road, Hull.
“It’s obviously a serious incident to have that many armed police.
“Please avoid the area if you can and thank you to Humberside Police for keeping us safe.”
More to follow…