A teenage boy was stabbed to death because his alleged attacker thought the 16-year-old was backing out of a $160 drug deal, a court has heard.

Ryan John Howes has pleaded not guilty to murdering Michael Brack, who died from a single stab wound after he bled out in a Bundall street, on Queensland's Gold Coast, in November 2015.

On the opening day of his trial, prosecutors told the Supreme Court in Brisbane that Michael had gone with friends to sell Mr Howes 14 grams of marijuana, but Mr Howes said he needed to go home and get money which made the teenager frustrated and anxious to leave.

Prosecutor Glen Cash told jurors witnesses would say Mr Howes "flipped out" and stabbed the teenager with a kitchen knife which almost severed an artery.

"He used that to strike Michael Brack … to the left side of the lower neck," Mr Cash said.

Mr Cash said the teenager bled to death "in a matter of minutes".

The court heard Michael's friends drove away from the scene because they were in fear of Mr Howes trying to get into the vehicle.

Michael died at the scene, despite neighbours coming to his aid and paramedics' attempts to revive him.

'He hooked it straight into Michael'

Ryan Howes has pleaded not guilty to murdering Michael Brack. ( ABC News )

Michael's friend Reece Rowe went to the drug deal with him and said Mr Howes "flipped out" and began yelling that they did not trust him.

"It was a bit of a blur, it happened so quick," he said.

"He hooked it straight into Michael. It looked like a punch at the time."

Mr Rowe said he threw the cannabis at Mr Howes and said "this is what you came for, take it".

The jury was told they would hear evidence from an undercover police officer who spoke to Mr Howes in the cells after he was arrested.

Mr Howes allegedly said he heard the click of a gun when he approached Michael at the vehicle.

Mr Cash said one of Michael's friends would give evidence that a few months before the death, he saw what appeared to be gun in the 16-year-old's room but "whether it was real or not, it wasn't functioning".

The court was told a key issue in the trial would be whether there was an intention to kill.

Accused learned about death from TV news

Mr Howes' former girlfriend Kyah Gallegos testified he returned home later that night with a knife.

"He walked in with a knife in his hand which had blood on it," she said.

She said the utensil had been broken in half.

Ms Gallegos told the court the pair saw the stabbing on the news.

"[He] put his hands behind his back and said we need to get the f*** out of here," she said.

The court heard Mr Howes was arrested by police in a roof cavity days after Michael's death.

Michael's family have attended the trial, which is scheduled to run for two weeks with up to 20 witnesses expected to give evidence.