Police fired into a group of opposition supporters outside Ghana's Supreme Court on Monday, hitting a bystander in the head, police confirmed.

Police told AFP that the victim, who had a bullet lodged in his head, had been taken to a military hospital for treatment.

A journalist said he saw police open fire on the supporters of the New Patriotic Party (NPP) who were awaiting a Supreme Court ruling on a heated dispute over voter identification.

The reporter for the independent Dispatch newspaper said several dozen police were at the scene, and that they had also used teargas to disperse the some 300 demonstrators.

The police fired "a lot" of shots into the crowd, and one man fell to the ground with a shot to the head as the protesters scattered for cover, the journalist said.

Mike Oquaye, political scientist at the University of Ghana, said he was inside the courtroom when he heard the shots outside.

Before the shooting, he said, "We could hear some people singing, but it was not disturbing the court."

The protesters had been chanting "No picture, no vote," insisting that old ID cards bearing only thumbprints should not be allowed because they would invite fraud in Thursday's presidential and parliamentary elections.

Speaking to AFP, some of the protesters awaiting the potentially explosive ruling warned that the elections could turn violent if the court rules that voters can use old voter IDs bearing only thumbprints if they failed to obtain new photo IDs issued under a donor-funded program that ended Sunday.

Richard Baoteng, 33, said: "I'll prevent the people who want to vote in my community (with thumbprint IDs). So that means violence. If the Supreme Court doesn't want violence, then they should say 'no picture, no vote'."

"We are prepared to vote with photo IDs. We are prepared for violence," said Baoteng, a mechanic.