Police are hunting for a group of attackers after a deadly shooting in the US city of Birmingham, Alabama, on Saturday night.

Four people were killed - of whom three have been formally identified - and 17 others were injured.

Investigators have described it as a "hit" that involved multiple gunmen who appeared to target a specific individual.

Here is everything we know about the incident so far.

What happened?

The attack unfolded just after 23:00 local time (05:00 BST) around Magnolia Avenue South, in the Five Points South nightlife district. Local media said it happened as patrons queued to enter a hookah and cigar lounge.

The shooting was characterised by Scott Thurmond, the Birmingham police chief, as "targeted" rather than a random incident.

A number of attackers are alleged to have got out of a vehicle and opened fire on a crowd in a public area before fleeing the scene.

They are alleged to have used "machine gun conversion devices". Investigators say they have collected about 100 shell casings from the scene, among other evidence.

Birmingham Mayor Randall Woodfin blamed "Glock switches" - devices that can be attached to handguns to make them fire automatically - and described these as the "number one public safety issue" in the area.

The hookah lounge, Hush, said it was "heartbroken" that its customers were caught up in the incident - which it stressed had nothing to do with the venue itself.

Who was killed and injured?

A woman and two men who were among the four people killed have been named by Birmingham police, who said they were local to the area:

Anitra Holloman, 21, from Bessemer

Tahj Booker, 27, from Birmingham

Carlos McCain, 27, also from Birmingham

The trio were pronounced dead at the scene by emergency officials. A fourth person, who died after being taken to hospital, has not been formally identified.

The person targeted in the "hit" was thought to be among those killed, Mr Thurmond said, without specifying who that individual was.

The police chief said investigators had received information to suggest that "someone was willing to pay money to have that person killed".

Police say 17 others were injured, revising down an earlier figure of 18. Their wounds varied in severity, some of them being life-threatening. Many were taken to hospital.

A 24-year-old man, Gabriel Eslami, told local news outlet Al.com he had been shot in the buttocks as he queued for the Hush lounge, and hospitalised himself.

He described seeing "blood everywhere" and the sight of "people's bodies laid out on the pavement".

What is known about the attackers?

No arrests have been made.

A search continues for the culprits, and little is known about them.

Police in believe, however, that the incident may stem from a murder-for-hire plot.

A reward has been offered for information on the suspects.

Other agencies have been helping with the investigation: the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) and the FBI.

More updates are expected on Monday.

What is the bigger picture?