The busy stretch of road near Edinburgh Airport has been closed in both directions between the Barnton junction and the roundabout at East Craigs.
It’s understood police shut the road after the accident took place at around 12.30am on Friday morning.
One eyewitness reported seeing “lots of emergency services” at the scene.
Drivers are have been warned to expect heavy congestion and to use an alternative route if possible.
A Police Scotland spokesman said: “At around 00.30 hours on Friday 25 May officers responded to a serious road traffic accident involving four vehicles on the A902 Maybury Road at the Barnton Interchange.
“Investigations are on going and the road will remain closed for some time.
“Officers are appealing for information. Anyone with information is asked to call 101”
A number of crews were at the scene before leaving at 2.42am.