Police are appealing for witnesses after reports of gunshots near the A8 after the vital link to Edinburgh Airport was closed both ways last night.
The road was shut between the airport and Newbridge while officers combed the scene following the incident, believed to be at Ratho Station.
Officers responded to initial reports of shots at a property near the road. No-one was injured during the incident.
Superintendent Matt Richards, of Police Scotland, said a team of officers were working on the inquiry and to provide high visibility patrols in the area. He also made an appeal for information to help with police investigations.
He said: “This incident took place close to one of the main routes to and from Edinburgh. It is always busy with passing traffic. I would appeal to any member of the public, either locally, or who may have been passing through Ratho Station at or around 9.30pm last night and who saw anything to contact us urgently.
“It is imperative that we trace the individual involved in this incident, which thankfully did not result in any injuries. The consequences of a weapon being discharged in the manner which happened last night may have been extremely serious.
“We believe that a firearm was discharged and that this was not a random act. We are keen to speak to any member of the public who saw or heard anything suspicious, or who thinks they may have information about those responsible. Anyone with any information can contact the 101 Police number or Crimestoppers, in confidence, on 0800 555 111.
“Uniformed officers are in the area to provide extra patrols to support the local community.”
Passengers missed flights as a result of heavy delays caused by the road closure.
Buses were diverted and commuters heading into the Capital from the west faced lengthy delays during the rush hour.
Lewy Parkinson tweeted the airport having missed a flight this morning. He said: “Due to incident on a8 arrived at 6:02am, bag chk in closes 6am. No leeway at security. V upset.”
Shauni Allan tweeted that she had been stuck in traffic for almost three hours. She said: “My last call for flight is 8.55 been stuck in traffic for nearly 3 hours what happens if I miss my flight?”
Later, she tweeted again: “Missed my flight, absolute disgrace.”
Another tweet from Drunk Alpinists said: “Good old Edinburgh traffic. Been on the newbridge roundabout slip road for 1.5hours. Moved 200m.”
A spokesman for the airport said they had implemented its “crisis mode” to ensure passengers were kept well informed throughout the night.
Regular updates were posted on the airport website and Twitter account with details of an alternative route.
Anyone travelling to and from the airport was advised to leave extra time and head towards Hermiston Gait (junction 1 on the M8) then follow signs for the airport.
The spokesman said: “We have been up most of the night keeping our website and Twitter updated. We have informed the airlines but unfortunately it is one of those things and the flights will have to stick to schedule.
“We have tried to make sure people are leaving as much time for their journeys as possible because the roads are incredibly busy.”
Edinburgh West Liberal Democrat MP Mike Crockart said: “It’s difficult to speculate without knowledge of the incident but having been a scenes of crime officer I have been to murder scenes that have taken less time than this.
“Shutting a major route into Edinburgh for what will be 14 hours seems excessive.
“Police say ‘use an alternative route’ when there isn’t one so it’s bound to lead to the congestion that places like Ratho have seen this morning.”