Twenty people were killed and more than two dozen injured in a shooting Saturday in a busy shopping area in the Texas border town of El Paso, the state’s governor said.

Meanwhile, the police chief said among the possibilities being investigated is whether it was a hate crime. Two law enforcement officials who spoke to The Associated Press on condition of anonymity identified the suspect taken into custody as 21-year-old Patrick Crusius of the Dallas area.

Police said another 26 people were injured, most of them being treated at area hospitals. Most of the victims were believed to have been shot at a Walmart near the Cielo Vista Mall, they said, adding that the store was packed with as many as 3,000 people during the busy back-to-school shopping season.

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President Donald Trump was briefed on the shooting Saturday afternoon and evening, according to Deputy White House Press Secretary Steven Groves.

Trump tweeted Saturday afternoon: "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!"

On Saturday evening, the president tweeted: "Today’s shooting in El Paso, Texas was not only tragic, it was an act of cowardice. 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…. ….Melania and I send our heartfelt thoughts and prayers to the great people of Texas."

Mexico President Andrés Manuel López Obrador said three Mexicans have been killed in the shooting in the border city.

He tweeted Saturday that he sends "condolences to the families of the victims, both American and Mexican."

Beto O’Rourke, the Democratic presidential candidate and former Texas congressman, arrived back in his hometown of El Paso on Saturday evening after leaving a campaign event in Las Vegas following news of the shooting.

In an interview on CNN, he thanked city workers and members of the community for their efforts and resolve. "El Paso is really showing up and standing up for our fellow El Pasoans," he said.

Texas Gov. Greg Abbott, who confirmed the number of victims at a news conference, called the shooting "a heinous and senseless act of violence" and said the state had deployed a number of law enforcement officers to the city.

"The scene was a horrific one," said El Paso Police Chief Greg Allen, who added that many of the injured had life-threatening injuries, according to the Associated Press.

He said police also had found a manifesto that Crusius, a white male student from Allen, Texas, may have written and posted online — one reason it was being investigated as a hate crime. The FBI has also opened a domestic terrorism investigation, CNN reported.

Residents were volunteering to give blood to the injured, while police and military members were trying to help people who were looking for missing loved ones.

Police responded in the midmorning to an active shooter scene at the Cielo Vista Mall, near Interstate 10 on the east side of the city, and were advising people to stay away from the area and to look for missing family members at a school being used as a reunification area.

Police said by midafternoon that a suspect was in custody and the public was no longer in danger. The suspect, who used a rifle, was arrested without incident. Police believe he was the "sole shooter" but are continuing to investigate reports that others were involved.

Ryan Mielke, a spokesman for University Medical Center of El Paso, said 12 people were brought to the hospital with injuries, including one that died. Two of the injured were children who were being transferred to El Paso Children’s Hospital, he said. He declined to provide additional details on the victims.

Eleven other victims were being treated at Del Sol Medical Center, according to hospital spokesman Victor Guerrero. He said those victims ages ranged from 35 to 82.

El Paso, which has about 680,000 residents, is in West Texas and sits across the border from Juarez, Mexico.

The mass shooting in came less than a week after a gunman opened fire on a California food festival. Santino William Legan, 19, killed three people and injured 13 others last Sunday at the popular Gilroy Garlic Festival, and died of a self-inflicted gunshot wound.