Police in the town are appealing for witnesses and information following the crash, which happened at around 6.05 pm.
Emergency services received a report of a head-on collision involving two cars near to The Pines Golf Course.
One man was taken to the Dumfries and Galloway Royal Infirmary where his condition was later described as ‘serious.’
Diversions were set up during the road closure.
A spokesman for Police Scotland said officers conducting enquiries into the circumstances are appealing for anyone at the location around the time of the crash to contact them at the Road Policing Unit in Dumfries on 101.