BUENOS AIRES (AFP) - An off-duty police officer opened fire at a busy nightclub in Argentina, killing a police commissioner and one other and injuring 15, authorities said on Saturday.

"It was a massacre," Mayor Marcos Berlota told news channel C5N, saying the shooter had gone to the club with his wife, then went back outside, got his gun from his car and "went back in and shot the police commissioner in the head".

The second victim, a truck driver, "was also killed by a shot in the face."

The officer, a man in his 40s with two children, then sprayed a score of bullets into the club, which was filled with young people.

The incident took place in the pre-dawn hours on Saturday in Naschel, a western town of 4,000 residents located 870km west of Buenos Aires.

"He went into the club and started shooting. There was no fight before," said Milagros Quiroga, 17, who described it as if "he was shooting animals".

San Luis state governor Claudio Poggi told another local news channel, TN, the officer, who had years on the job, had used his service weapon.

He said the injuries varied in severity, with many admitted to various hospitals in the region.

The incident ended when the shooter, who had left the club and walked a few meters away, where the police station was located, was shot in the leg by an officer on guard.

The motive behind the shooting was unclear.