A mass shooting involving several assailants has left at least four people dead and dozens wounded in the US state of Alabama, police said on Saturday.

"We believe that multiple shooters fired multiple shots on a group of people" in the Five Points South district of Birmingham just after 11:00 pm, police officer Truman Fitzgerald told local media.

Officers found two adult males and one adult female who was unresponsive on the sidewalk suffering from a gunshot wound, Fitzgerald said. All three were pronounced dead at the scene.

A fourth victim died at a local hospital, he added.

Dozens of people were wounded in the shooting with at least four sustaining life-threatening injuries, Fitzgerald said.

The others had "various injuries", he added.

Police have not got anyone in custody over the shooting, Fitzman said, urging the public to provide any information that could help the investigation.

Several agencies are involved in the investigation, including the Federal Bureau of Investigation and the Bureau of Alcohol, Tobacco, Firearms and Explosives.

Fire rescue services at on the scene Saturday night and had cordoned off the area.

This year, there have been at least 403 mass shootings -- defined as a shooting involving at least four victims, dead or wounded -- across the United States, according to the Gun Violence Archive.

At least 12,416 people have been killed in firearms violence this year in the United States, according to the GVA.