The route is closed in both directions.
Police were called at 7:45 following reports of a crash involving a car and a lorry. A police spokesperson said: “Police in Midlothian are currently in attendance on the A702, near Boghall farm, following a serious collision involving a car and an HGV which took place at around 7.45am on Tuesday August 7.
The diversion heading southbound commences on the A702 at Hillend.
Drivers can leave by taking left onto the A703 at Hillend continuing on the A703 for approx 2 miles to Plover Hall roundabout at the A701 junction.
By turning right to follow the A701 southwards, for about 3 miles they can get into Penicuik.
By going right at the A766 junction they can follow the A766 to re-join the A702 near Ninemileburn.
Local southbound A702 traffic arriving at Easter Howgate will be directed to take left to follow the unclassified road to Gowkley Moss roundabout to join the diversion route.
Heading northbound the A702 is closed at the A766 junction near Ninemileburn - Drivers are being instructed to leave the A702 by taking the right onto the A766 north of Ninemileburn - following the A766 into Penicuik - before turning left onto the A701 then travelling north for approx.
They then travel 3 miles to Plover Hall roundabout at the A703 junction before following the A703 for approx.
After 2 miles they can then rejoin the A702 at Hillend.