At least 22 people were shot -- two who were killed instantly -- early Sunday when three assailants unleashed a barrage of gunfire on a crowd standing outside a birthday party concert at a rented banquet hall in suburban Miami, police said.

The shooters, armed with high-powered rifles and handguns, arrived and fled in an SUV that police were still searching for Sunday evening. The gunmen waited outside the party for about 40 minutes before opening fire just as revelers were leaving the celebration, Miami-Dade Police Director Alfredo "Freddy" Ramirez told ABC News on Sunday afternoon.

About 100 shell casings were collected at the scene by investigators, Ramirez said, adding that some party-goers under attack returned fire.

The motive for what Ramirez described as a "cowardly act" remains under investigation.

Three of the wounded victims are in critical condition and two of them are on life support, Ramirez said.

No arrests have been made in what was the 17th mass shooting in the United States in May alone, and the second to rock the Miami area since the start of Memorial Day weekend, according to the Gun Violence Archive, an online website that tracks shootings across the country.

On Friday, one person was killed and six were injured in a drive-by shooting in Miami's Wynwood arts district. That came two days after nine people were killed in a workplace shooting in San Jose, California, in which the suspect died by suicide.

The latest carnage in what officials, including President Joe Biden, have called a gun-violence "epidemic" in America, occurred between midnight and 1 a.m. Sunday in an unincorporated area of Miami-Dade County near Hialeah, about 11 miles northeast of Miami.

The deadly fusillade erupted when a white Nissan Pathfinder pulled up to the El Mula banquet hall that was being rented for a birthday concert for a local rapper, three armed occupants exited the vehicle, aimed at the crowd and fired, according to preliminary information from a law enforcement briefing that was reviewed by ABC News. Ramirez said investigators suspect the gunmen waited patiently nearby before committing the ambush.

"This is a despicable act of gun violence," Ramirez said at a news conference early Sunday. "This is targeted. This is definitely not random."

Ramirez said investigators are combing through surveillance footage of the incident, hoping to identify the attackers.

Ramirez called it "a terrible tragedy for the community" and offered condolences to the families of those killed.

Two victims were pronounced dead at the scene, while eight injured people were taken to hospitals by ambulance and more than a dozen of those hurt were rushed to hospitals in private cars, according to the Miami-Dade Police Department. Investigators are monitoring hospitals for other possible victims.

Angelica Green told ABC affiliate station WPLG-TV in Miami that her 24-year-old son was among those who were injured.

"He called us in ... frantic, telling us he had been shot, that it hurts, that he loves us," Green said. "My husband is like, 'No, stay with us. Stay with us.'"

Green said her son was shot in the stomach.

PHOTO: A Miami-Dade police officer stands near where a mass shooting took place outside of a banquet hall on May 30, 2021 in Hialeah, Florida. (Joe Raedle/Getty Images)

"He said the guys came with ski masks and hoodies and just started shooting up the crowd," Green said.

None of the suspects are in custody and detectives are asking for assistance from witnesses in identifying them and their whereabouts.

"I am at the scene of another targeted and cowardly act of gun violence, where over 20 victims were shot and 2 have sadly died," Ramirez added in a statement posted on Twitter. "These are cold-blooded murderers that shot indiscriminately into a crowd and we will seek justice."

Anyone with information regarding this incident is urged to contact CrimeStoppers at (305) 471-TIPS (8477) or (866) 471-8477.

 abcnews.go.com