At least four people have been killed and 18 injured in a mass shooting in Birmingham, Alabama, police say.

“Multiple shooters fired multiple shots on a group of people” late on Saturday in the Five Points South area of the city, Birmingham Police officer Truman Fitzgerald said.

Officers found the bodies of two men and one woman at the scene, while a third man later died of bullet wounds in hospital, Birmingham Police said

The culprits are believed to have approached the scene in a vehicle before getting out and opening fire. No suspects have been arrested.

Mr Fitzgerald added that they believed the shooting was "not random and stemmed from an isolated incident where multiple victims were caught in the crossfire".

The shooting may have been a result of a murder-for-hire plot, Police Chief Scott Thurmond was quoted as saying by local news outlet Al.com.

The intended target was among those killed, Mr Thurmond said at a news conference on Sunday.

“It wasn’t the location, it was the person, so wherever the person was was where it was going to take place, wherever they can catch that individual,’’ Mr Thurmond said. "That’s just where they happened to catch them.”

The other victims - all of whom were standing outside - are so far believed to have been caught in the gunfire.

Four of the injured suffered life-threatening wounds, according to Mr Fitzgerald.

The BBC has contacted the Birmingham Police Department for comment.

Authorities are also pressing to find the shooters.

The police said in a statement that they are working with the FBI and other federal agencies, are offering a $5,000 reward for information and have opened a web portal for submitting photos and videos of the incident.

The Five Points South district is known for its nightlife. The shooting occurred on Magnolia Avenue, Mr Fitzgerald said.

Witnesses who were queuing outside a hookah and cigar lounge on Magnolia Avenue at the time told local news site Al.com that some of the gunfire sounded as though it came from a gun converted to be fully automatic.

Earlier on Sunday, Mr Fitzgerald had told reporters there were "dozens of gunshot victims" after the incident.

Birmingham Mayor Randall Woodfin blamed "Glock switches" - devices that can be attached to handguns to make them fire automatically - for the violence, posting on social media on Sunday that they "are the number one public safety issue in our city and state".

"Converting a semi-automatic weapon into a fully automatic weapon that discharges all bullets within seconds doesn’t belong on our domestic streets," he wrote, adding that the city does not have the power to outlaw Glock switches, only the state.

He told CNN later on Sunday that more than 100 shell casings had been found at the crime scene.

There have been more than 400 mass shootings across the US so far this year, according to the Gun Violence Archive, which defines a mass shooting as an incident in which four or more people are injured or killed.

The incident in Birmingham is the second mass shooting to place in the city in a two-month period, and the third quadruple homicide of 2024, according to Al.com.