A single-decker bus collided with a parked car, a van, and a tree, leaving the bus "completely mangled", one witness said.
One man, a passenger, suffered potentially serious injuries and was taken to Heartlands Hospital after being cut free from the bus.
Emergency services were called to Hawthorn Road, Kingstanding, at 7:25am.
A resident living near the scene said: "I heard a loud bang, then a wallop, at around 7am.
"I came outside and a lot of people were on the street and the bus was where you see it now.
"It's a huge crash but i've been told by the officers here that everyone is OK, including the driver."
"HART paramedics, two paramedic officers, a MERIT trauma doctor and critical care paramedics together with two ambulance crews attended the scene.
"Eight occupants of the bus were assessed, three were uninjured and discharged on scene.
"The five remaining patients, the bus driver and four passengers, received further assessment and treatment on scene by the team of ambulance staff.
"A male passenger sustained potentially serious injuries and received treatment by ambulance staff before being conveyed to Heartlands Hospital for further care.
"The driver, a man, along with a passenger, a woman, were conveyed to Good Hope Hospital with less serious injuries for further checks.
"A second woman was assessed and conveyed to Heartlands Hospital for further precautionary checks. A third woman was discharged on scene."
Meanwhile, West Midlands Police added: "We were called following a collision between a bus and two vehicles at around 7:25am today.
"Six people suffered minor injuries and enquiries around the collision continue."
National Express West Midlands said: "A National Express West Midlands bus on the 28 service was involved in an incident this morning (Tuesday 9th August) on Hawthorn Road near Perry Common.
"Emergency services attended the scene and we will continue to give them every assistance, as well as carrying out a full investigation of our own into what happened.
"Our 28 services are currently on diversion from Perry Common Road. We advise customers to check our social media channels for the latest updates to services and apologise for any delay to their journeys."
West Midlands Fire and Rescue Service added: "At 7.26 on August 9, crews from Perry Barr and Erdington were called to an RTC on Hawthorne Road.
"The incident involved a single-decker bus which had collided with a parked car and van.
"A woman and the driver of the bus were both led to safety by our crews and were due to be conveyed to hospital for further precautionary checks.
"A further one man, who was trapped by injuries on the bus, was extricated from the bus by firefighters using Holmatro cutting equipment.
"His injuries are not thought to be life-changing, but he too will be conveyed to the hospital for a further check.
"The car and bus were made safe by fire service crews. The local council highways department has also been in attendance and will re-attend later once West Midlands Police have concluded their investigations.
"Hawthorn Road remains closed for police to carry out their investigations and the incident has been left in their care."