Willie McCoy had been recording at a family member's home when he decided to go to a Taco Bell restaurant

A young US rapper shot dead by police in northern California earlier this month after he was found slumped over in his car was struck by around 25 bullets, a family lawyer said on Wednesday.

Melissa Nold told AFP that six police officers shot Willie McCoy -- who used the stage name Willie Bo -- in the face, throat, chest, right ear, arms and shoulders on February 6 in the town of Vallejo.

"This was overkill," said Nold, who examined McCoy's body at the mortuary.

"There is no evidence to justify that level of force and no possible reason why you would need to shoot anybody that many times.

"It's almost like they were doing target practice," she added.

Nold said McCoy, 20, had been recording at a family member's home when he decided to go to a Taco Bell restaurant late in the evening.

Police said employees called them to report a Mercedes-Benz parked in the drive-thru line with the engine running and a man slumped over the steering wheel.

Officers said they noticed a gun in the car and as they were assessing the situation, McCoy woke up and reached for the firearm, ignoring orders to "put his hands up."

"Fearing for their safety, six officers fired their duty weapons," the Vallejo Police Department said in a statement.

Authorities said the gun retrieved from the car was fully loaded and had been reported stolen in Oregon.

Nold, herself a former police officer, described the response as "the kind of force you use in a shootout."

She added that the officers could have taken a position of cover behind their own cars and used a siren or a bullhorn to awaken McCoy.

"If he was supposed to be armed, why would you stand in front of him?" she said.

The Vallejo Police Department said they had no further comment on Wednesday.

McCoy's shooting follows a string of similar incidents of alleged police brutality in the US in recent years.

And this is not the first time the Vallejo Police Department has come under scrutiny following complaints of excessive force.

In 2017, a video of an officer straddling a man on the ground and punching him in the face several times prompted an uproar.

Another video last year showed a Vallejo police officer repeatedly hitting a man with his flashlight as another officer restrained and handcuffed him.