EL PASO, Texas (Reuters) - A man armed with a rifle opened fire at a Walmart store in El Paso, Texas, on Saturday, killing 20 people and wounding 26 others as panicked shoppers and employees scurried for cover before the gunman surrendered to police at the scene.

Many shoppers in the busy store were buying back-to-school supplies when they found themselves caught up in the latest mass shooting to rock the United States, just six days after a teenage gunman killed three people at a summer food festival in Northern California.

Saturday’s suspect was officially identified as a 21-year-old white male from Allen, Texas, a Dallas suburb some 650 miles (1,046 km) east of El Paso, which lies along the Rio Grande, across the U.S.-Mexico border from Ciudad Juarez.

Citing law enforcement officials, multiple news media reports named the suspect as Patrick Crusius.

El Paso police chief Greg Allen said authorities were examining a manifesto from the suspect indicating “there is a potential nexus to a hate crime.” Officials declined to elaborate and said the investigation was continuing.

But a four-page statement posted on 8chan, an online message board often used by extremists, and believed to have been authored by the suspect, called the Walmart attack “a response to the Hispanic invasion of Texas.”

It also expressed for support for the gunman who killed 51 people at two mosques in Christchurch, New Zealand, in March.

CNN reported that the FBI has opened a domestic terror investigation into the Texas shooting.

El Paso and Ciudad Juarez, together with the neighboring city of Las Cruces, New Mexico, form a metropolitan border area of some 2.5 million residents constituting the largest bilingual, bi-national population in North America.

Mexico’s President Andres Manuel Lopez Obrador said three Mexican nationals were among the dead, and six others were among the wounded.

The carnage ranked as the eighth-deadliest mass shooting in modern U.S. history, after a 1984 shooting in San Ysidro, California, that claimed 21 lives.

“We are going to aggressively prosecute it both as capital murder but also as a hate crime, which is exactly what it appears to be,” Texas Governor Greg Abbott told reporters, adding, “I don’t want to get ahead of the evidence.”

(Graphic: Mass shootings in the United States - tmsnrt.rs/2KefvTT)

SUSPECT SURRENDERED

Details of how the shooting unfolded were not immediately clear. But video footage from the scene showed victims lying on the ground inside and outside the store. One shopper told Reuters the gunshots sounded like they began outside the building.

The suspect surrendered to police as officers closed in on him, and he was taken into custody without incident, authorities said. Video posted on social media appeared to show him being handcuffed by police and placed in a squad car.

El Paso Mayor Dee Margo said police responded to the shooting within six minutes.

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Citing a law enforcement source, El Paso television station KTSM published on its website what it said were two photos of the suspect taken by security cameras as he entered the Walmart.

The images showed a young man wearing eyeglasses, khaki trousers and a dark T-shirt, wielding an assault-style rifle. He appeared to be wearing headphones or ear protection. Reuters could not immediately verify the authenticity of the images.

On Twitter, U.S. President Donald Trump branded the shooting “an act of cowardice,” adding, “I know that I stand with everyone in this Country to condemn today’s hateful act. There are no reasons or excuses that will ever justify killing innocent people.”

About half of the injured, including at least two children, were initially taken to the University Medical Center of El Paso, where a number of the victims remained in surgery hours later, hospital spokesman Ryan Mielke said.

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‘PEOPLE WERE PANICKING’

Officers from several law enforcement agencies raced to the scene at the Walmart and nearby Cielo Vista Mall, including local police, state troopers, Homeland Security agents and border patrol.

Shoppers fled for their lives, including Kianna Long who was at the Walmart with her spouse when they heard gunfire.

“People were panicking and running,” Long said. “They were running close to the floor, people were dropping on the floor.”

Her husband, Kendall, said the sound of gunfire seemed to move indoors after initial shots that he heard coming from outside.

The couple sprinted through a stock room at the back of the store before huddling with other customers in a steel container in a shipping area.

Glendon Oakley, an off-duty soldier who was in the store, told KTSM-TV that he and another man rounded up children they saw running in terror without their parents and hustled them to safety.

In the shooting’s aftermath, Walmart and adjacent businesses, including the mall and a movie theater, were closed as police conducted an initial search for additional possible suspects. Authorities later said the gunman had acted alone.

Local media said there was such an overwhelming response to appeals for blood donations that long lines formed at medical centers, where some would-be donors were asked to return on Sunday.

The tragedy in El Paso came just six days after a teenage gunman opened fire with an assault-style rifle on a crowd attending the annual Garlic Festival in Gilroy, California, killing three people and injuring a dozen others before he was shot by police and ultimately took his own life.

At a Democratic presidential candidate forum in Las Vegas a clearly emotional Beto O’Rourke, a former Texas congressman who is from El Paso, broke the news to the audience about the deadly mass shooting in his home city.

Addressing reporters, he teared up and struggled to deliver a short statement.

“I am incredibly saddened and it’s very hard to think about this,” he said. “El Paso is the strongest place in the world. This community is going to come together. I’m going back there right now to be with my family, to be with my home town.”

Several other Democratic presidential contenders joined in condemning the rise of mass shootings, with Pete Buttigieg declaring: “America is under attack from homegrown white nationalist terrorism.”