Two motorcyclists are in hospital with serious injuries after separate crashes in the north-east.
A 31-year-old man is in a serious but stable condition, after the offroad motorbike he was driving collided with a car on Union Grove in Aberdeen yesterday afternoon.
A 30-year-old man who was driving the car - a Mercedes GLA - was also taken to hospital but later released.
Constable Lorcan Thame of the road policing unit at Inverurie said: "Our investigation is ongoing to establish the cause of this crash and we are appealing for any witnesses, who have not yet spoken to police, to come forward.
"From initial inquiries, we have been told that there were a number of off-road motorbikes being driven round the local area at the time of the crash and we are working to trace the other riders.
"We have been speaking to witnesses and viewing CCTV footage to gather more details on the circumstances surrounding this crash.
"Anyone who was in the area who witnessed the crash, or who has any information on the off-road bikes or saw them being driven nearby is asked to contact officers through 101 quoting reference number 2237 of May 27."
Meanwhile a 37-year-old man was airlifted to Aberdeen Royal Infirmary last night, after being thrown from his red BMW motorbike on the A93 Braemar to Glenshee road, near Newbigging.
Officers say the bike appeared to lose control at around 7.50pm.
His condition is described as critical.
Sergeant Peter Henderson said: "I am appealing to anyone who was on the road around the time of the crash to contact us as there may be information which could help us establish the exact circumstances of what has happened.
"In particular, if any motorists have dash cams, please check your footage as it may assist in our investigation."
Anyone with information is asked to call officers via 101, quoting incident number 3481 of May 27.