Wolverhampton Road, between the junctions of Broadway and Brandhall Road, was been closed while emergency services attend the crash which involved two cars and happened at around 2pm on Wednesday.
An Audi overturned and ended up on a grass verge next to the dual carriageway, while a Kia was left crumpled and surrounded by debris in the road.
Two women - one from each car - had to be cut free by firefighters and bystanders rescued an 18-month-old girl from the Kia.
The woman who was in the Kia with the toddler suffered "very serious injuries" and was rushed to hospital in a critical condition by ambulance, a West Midlands Ambulance Service spokesman said.
The toddler was also taken to hospital but her injuries are not believed to be life-threatening.
Meanwhile the woman trapped in the overturned Audi received treatment for "potentially serious injuries" before being taken to Birmingham's Queen Elizabeth Hospital.
Motorists were advised to avoid the area if possible, with emergency services on the scene several hours later.
A West Midlands Ambulance Service spokesman said: “Crews arrived to find two cars that had suffered significant damage in the collision.
“From the first car, a woman had to be cut free with the help of the fire service.
"She was treated for very serious injuries by ambulance staff before being taken to Queen Elizabeth Hospital by land ambulance in a critical condition.
"A doctor travelled on the back of the ambulance to continue treatment on route.
“A female toddler had been freed from the car by bystanders prior to the arrival of ambulance resources.
"She was assessed and treated for injuries not believed to be life-threatening before being taken to Birmingham Children’s Hospital by land ambulance.
“The fire service had to cut a second woman free from the other car involved in the incident, which had overturned.
"She received treatment for potentially serious injuries before also being taken to Queen Elizabeth Hospital by land ambulance.
"Again, a doctor travelled with her on her journey to help continue treatment.”
A West Midlands Fire Service spokesman said: "The incident involved two cars in a collision on Wolverhampton Road. There were three people in the two vehicles.
"One girl, aged 18 months, and a 25-year-old woman were in the Kia, while a 30-year-old woman was in the Audi.
"The baby was rescued from the vehicle – and was being treated by paramedics and taken to Birmingham Children's Hospital.
"The two females were trapped in the vehicles and firefighters were using cutting equipment to free them.
"Both were being taken to the Queen Elizabeth Hospital by land ambulance.
"We had 13 firefighters at the scene, police and ambulance were also in attendance."
A West Midlands Police spokesman urged motorists to avoid the area in the aftermath.
West Midlands Ambulance Service sent three ambulances, two paramedic officers, the trust’s Hazardous Area Response Team, the Midlands Air Ambulance Critical Care Car, a BASICS doctor and the Warwickshire and Northamptonshire Air Ambulance to the scene.