(EL PASO, TX) — Twenty people were killed and dozens more injured on Saturday morning in a massacre at an El Paso, Texas, Walmart packed with back-to-school shoppers, making it one of the ten deadliest mass shootings in U.S. history, officials said.

The wounded ranged in age from a 2-year-old child to an 82-year-old victim.

The suspect was identified by authorities as Patrick Crusius, 21, of Allen, Texas.

He was “taken into custody without incident” and without any law enforcement officers firing their weapons, according to El Paso Police Department Sgt. Robert Gomez. The alleged shooter’s motives remains unknown, Gomez said.

Police initially said that there may have been “multiple shooters,” but Gomez later clarified that arrested just one person.

“At this time, we do have one person in custody. We don’t believe there’s anybody outstanding,” he said.

At a news conference on Saturday night, El Paso police Chief Greg Allen said that 20 people had died and 26 more had been injured — making the El Paso massacre one of the top ten deadliest shootings in U.S. history.

Allen said that law enforcement officials were reviewing a manifesto posted by the alleged shooter and that the massacre was being investigated as a possible hate crime.

The majority of the victims were shot inside the Walmart, according to Gomez, which at the time contained more than 100 employees and what authorities have preliminarily estimated to be between 1,000 and 3,000 Saturday morning back-to-school shoppers.

A spokesperson for El Paso’s Del Sol Medical Center said that 11 victims ranging in age from 35 to 82 were being treated at the facility. University Medical Center of El Paso received an additional 13 victims — two of whom were children, ages 2 and 9, who were stabilized and transferred to El Paso Children’s Hospital, according to officials. A hospital spokesperson said that nine patients were in critical condition and three had life-threatening injuries.

At 2 p.m. local time, the El Paso Police Department issued a tweet making an urgent request for blood donations, and directing local residents to two facilities run by Vitalent Blood Services where they could donate blood. Within three hours, photos posted to social media showed lines stretching around the block at locations accepting local blood donors.

‘On a mission’

Allen, the police chief, said the first 911 call came in at 10:39 a.m. local time, and that emergency responders were on the scene at 10:45.

The shooting began in the parking lot outside the Walmart, according to an eyewitness who said she heard gunshots as she drove through the parking lot with her mother.

Shopper Vanessa Saenz described the shooter in an interview with ABC News Radio as dressed in cargo pants and a black t-shirt, wearing ear protectors and said he looked like he was “dancing.”

Moments later, Saenz saw a woman a few feet away fall to the ground.

She then described seeing victims near the shooter who became cornered — with nowhere to run — and then watched the gunman raise a rifle, aim it at them and start firing.

“One thing I’ever never forget is when he walked into Walmart very confidently, like he was on a mission,” she later told ABC News anchor Tom Llamas in an interview for “World News Tonight.”

At 12:11 p.m. local time, the El Paso Police Department had issued a tweet that said in part, “We have multi reports of multiple shooters.”

Area residents were urged by local law enforcement to avoid the area north of the I-10 highway area in east El Paso.

Scene is still Active. We have multi reports of multiple shooters. Please avoid area police conducting search of a very large area. Media staging will be given when area is secure.

— EL PASO POLICE DEPT (@EPPOLICE) August 3, 2019

The Walmart is located at the Cielo Vista Mall, one of the city’s most popular malls, particularly among Mexican tourists who cross the U.S. border to shop there before returning to Mexico.

We’re in shock over the tragic events at Cielo Vista Mall in El Paso, where store 2201 & club 6502 are located. We’re praying for the victims, the community & our associates, as well as the first responders. We’re working closely with law enforcement & will update as appropriate.

— Walmart (@Walmart) August 3, 2019

Walmart issued a statement about the shooting on the retailer’s Twitter account.

“We’re in shock over the tragic events at Cielo Vista Mall in El Paso,” the statement said. “We’re praying for the victims, the community & our associates, as well as the first responders. We’re working closely with law enforcement & will update as appropriate.”

A spokesperson for El Paso’s Del Sol Medical Center said that 11 victims ranging in age from 35 to 82 were being treated at the facility. Unversity Medical Center of El Paso received an additional 13 victims — two of whom were children, ages 2 and 9, who were stabilized and transferred to El Paso Children’s Hospital, according to officials.

In El Paso, the Texas Dept. of Public Safety is assisting local law enforcement & federal authorities to bring this tragedy to the swiftest & safest possible conclusion. We thank all First Responders for their courageous response & urge all area residents to remain safe. https://t.co/H6UDwu81SY

— Greg Abbott (@GregAbbott_TX) August 3, 2019

At 11:35 a.m local time, the Dallas office of the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) issued a tweet saying ATF agents were responding as well.

By 2 p.m. local time, the El Paso Police Department had issued a tweet making an urgent request for blood donations, and directing local residents to two facilities run by Vitalent Blood Services where they could donate blood.

Blood needed urgently. Multiple injured transported to various hospitals. Blood donation centers Vitalent Blood Services at 424 s Mesa Hills and 133 N Zaragoza

— EL PASO POLICE DEPT (@EPPOLICE) August 3, 2019

At 11:35 a.m local time, the Dallas office of the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) issued a tweet saying ATF agents were responding as well.

Texas Gov. Greg Abbott said in a tweet that the state’s Department of Public Safety was responding to assist “local law enforcement & federal authorities to bring this tragedy to the swiftest and safest possible conclusion.”

Rep. Veronica Escobar, who represents Texas’s 16th Congressional District, tweeted that she is “utterly heartbroken by the developing news in El Paso.”

President Donald Trump has been briefed on the shooting and is monitoring the situation, according to White House Deputy Press Secretary Steven Groves.

In a tweet, the president said he had spoken with Gov. Abbott and pledged “total support of Federal Government,” before ending the message ‘God be with you all!’

Terrible shootings in ElPaso, Texas. Reports are very bad, many killed. Working with State and Local authorities, and Law Enforcement. Spoke to Governor to pledge total support of Federal Government. God be with you all!

— Donald J. Trump (@realDonaldTrump) August 3, 2019

Democratic presidential candidate and fellow Texan Beto O’Rourke told reporters he was in communication with local officials and was flying back home from an event in Nevada.

“I just ask for everyone’s strength for El Paso right now, everyone’s resolve to make sure that this does not continue to happen in this country,” he said. “But I’ll tell you, El Paso is the strongest place in the world.”

Copyright © 2019, ABC Radio. All rights reserved.