One appliance and crew from Gerrards Cross and two from Hillingdon attended, along with an officer.
Seven cars were on the hard shoulder and slip road of the motorway when they arrived.
Six women, four men, three girls and three boys were travelling in the cars.
The firefighters provided immediate emergency care to two women, before passing them into the care of South Central Ambulance Service. No one else is believed to have been injured.
The firefighters made the scene safe.
National Highways, and Thames Valley Police also attended.
The motorway was partially closed while emergency services worked at the scene.
