Gavin McKinnell, 33, ran to the black Vauxhall which he told another man at the scene had “misjudged” a corner.
Jurors heard how the pair were then warned to get back as flames engulfed the vehicle.
McKinnell is on trial at the High Court in Glasgow. He is charged with causing the deaths of Shaun Boyce, 27, and Storm Drummond, 25, by dangerous driving on the A711 Dalbeattie to Dumfries road in April 2017.
Prosecutors made a number of accusations including a claim that he did “engage in a race” with Mr Boyce.
Mr Boyce is said to have lost control of his car before striking a tree and barrier with the vehicle eventually catching fire.
Mr Boyce and his passenger Miss Drummond are said to have been so severely injured that they died.
McKinnell, of Dumfries, denies the charge.
Witness Connor Cameron, 25, yesterday told how he had been in his cottage close to the scene when he heard an “explosion” nearby.
He recalled: “When I walked outside, I could hear shouting, someone calling for ‘help’. It was a male voice.
“I told my wife to call an ambulance and I ran. I could tell something was not right. Someone was shrieking for help. It was not nice.”
Mr Cameron said he went on to discover a “smashed” Vauxhall, which was already on fire.
He added McKinnell was also there. Mr Cameron knew him from the local area.
Prosecutor Greg Farrell asked: “When you saw him, where was he?”
Mr Cameron: “He was frantically running around shouting help and trying to get into the car.
“I said ‘what has happened?’ He said the car had tried to overtake before the corner, misjudged it and had gone into the barrier. Both of us were then trying to run round the car to see if there was anything we could do.”
The witness said within 45 seconds to a minute the car was fully on fire.
He was not able to find out if anyone was inside.
Jacqueline Kerr said she had been in a car in the area when two vehicles went past.
McKinnell’s QC Thomas Ross asked her: “You thought the two of them were a pair of idiots ... that the two of them were acting badly?”
Miss Kerr said: “Yes.”
The trial continues.