West Midlands Police said a number of people were injured in knife attacks in the city centre at around 12.30am.
In a statement, West Midlands Police said: “We can confirm that at approximately 12.30am today we were called to reports of a stabbing in Birmingham city centre.
“We immediately attended, along with colleagues from the ambulance service. A number of other stabbings were reported in the area shortly after.
“We are aware of a number of injured people, but at the moment we are not in a position to say how many or how serious. However, all emergency services are working together at the scene, and making sure that those who are injured receive medical care.
“This has been declared a major incident.
“Work is still going on to establish what has happened, and could take some time before we are in a position to confirm anything.
“At this early stage it would not be appropriate to speculate on the causes of the incident.
“The emergency services have well-rehearsed plans for dealing with major incidents. Our response is ongoing in Birmingham city centre and will be for some time. Cordons are in place, and there are some road closures.
“Your safety is our priority. We are now reviewing our policing across the city and will make any necessary changes. You may see a greater police presence in the area.
"We would urge you to remain calm but vigilant and to stay away from the area.”