It is understood that the bus fire caused the closure westbound after Old Craighall.
However, Traffic Scotland reported just after 11am that lane 2 (of 2) is now open on the Edinburgh City Bypass westbound at Millerhill.
There are no reported injuries at this moment in time, according to Police Scotland.
It is not yet known how the bus caught fire.
Traffic Scotland had advised motorists to use an alternative routes and to take care when passing eastbound earlier this morning due to 'heavy smoke’.
A Police Scotland spokesperson said: “We were made aware of a bus on fire on the A720 Edinburgh City Bypass near the Millerhill Junction around 10.30am on Tuesday, 18 January.
"There are no reported injuries and the road is currently closed, with emergency services at the scene.”
Scottish Fire and Rescue Service spokesperson said: "We were alerted at 10.26am on Tuesday, January 18 to reports of a fire affecting a bus on the Edinburgh City Bypass, A720, Westbound between Old Craighall and Sheriffhall Roundabout.
"Operations Control mobilised three appliances to the scene to extinguish the fire and make the area safe.
"There were no reported casualties."