EL PASO, UNITED STATES (AFP, WASHINGTON POST, AP, REUTERS) - At least 20 people were killed and 40 injured in a shooting at a Walmart and neighboring stores in El Paso, Texas on Saturday afternoon (Aug 3) that sent shoppers racing for cover in a chaotic scene and prompted a massive police and medical response, local authorities and government officials said.

At least 23 are still being treated in hospitals, the authorities said.

The governor of Texas confirmed that 20 people had been killed in the shooting.

Six of the 20 people killed in the mass shooting in the US city of El Paso were Mexican nationals, Mexico's President Andres Manuel Lopez Obrador announced Sunday.

"Unfortunately it is confirmed that there are six Mexicans who lost their lives," the Mexican president said during a public ceremony in Michoacan state a day after the shooting.

Mexico's deputy foreign minister for North America Jesus Seade, wrote on Twitter, "The modern world can't allow such acts of XENOPHOBIC BARBARISM, which don't happen in a vacuum. CEASE completely the RHETORIC that incites them."

One official said that the specific number of people killed and wounded was subject to change, noting that some of the victims were critically wounded.

Two law enforcement officials familiar with the inquiry, who spoke on the condition of anonymity to discuss an ongoing investigation, identified the suspect as Patrick Crusius, a 21-year-old man from a suburb near Dallas. He was taken into custody without incident.

After speaking to the governor of Texas, President Donald Trump wrote on Twitter that the "reports are very bad, many killed" while several Democrats hoping to defeat him at next year's elections said it was past time to tackle an "epidemic" of gun violence.

It was the second fatal shooting in less than a week at a Walmart store in the US and comes after a mass shooting in California last weekend.

Footage shot on camera phones appeared to show multiple bodies lying on the ground in the store's carpark.

Other footage showed terrified shoppers running out of the store as gunfire echoed.

El Paso authorities have made a desperate appeal for blood donations.

VICTIMS AGED TWO TO 82 YEARS

Although police held off on announcing an exact figure, the NBC network reported 19 were killed and 40 wounded. CBS quoted the Texas attorney-general as saying between 15 and 20 were dead while law enforcement sources told ABC News that at least 18 people were killed.

"I can confirm there have been fatalities. I cannot confirm how many," Sergeant Robert Gomez of El Paso police told reporters.

"There have been injuries, there were several injuries. I don't have those numbers as of right now."

Sgt Gomez said that Walmart was "at capacity" at the time of the shooting, with 1,000 to 3,000 customers inside.

Various news reports said the ages of victims being treated at hospitals ranged from two to 82 years.

After officials initially said three people had been detained, Sgt Gomez confirmed that one person was in custody.

"I can confirm that it is a white male in his 20s," he told reporters.

"We believe he's the sole shooter."

A witness who gave her name as Vanessa said she had just pulled into the carpark at Walmart when the shooting began.

"You could hear the pops, one right after another and at that point as I was turning, I saw a lady, seemed she was coming out of Walmart, headed to her car. She had her groceries in her cart and I saw her just fall," she told Fox News.

The witness told Fox that she had seen a man wearing ear muffs open fire.

"He was wearing a black T-shirt, camo coloured pants. He was wearing something to cover his ears, like headphones, really thick ones.

"He was carrying a dark rifle and he was just pointing at people and just shooting and, yeah, the last thing I saw, he shot somebody that was in a corner."

After seeing the woman fall in the carpark, "that's when I thought, okay, this is not - these aren't fireworks... He was just shooting randomly. It wasn't to any particular person. It was any that would cross paths".

'HOW YOU DOING, BROTHER'

Video captured by a witness in the carpark at Walmart in the immediate aftermath of the shooting, aired on CNN, showed three people lying motionless on the ground.

One had fallen next to a truck, while two were on the pavement outside the store entrance. "Ambulance! Help!" people cried as they rushed to the victims.

"How you doing, brother, how you doing?" one man was heard saying on the recording.

A still captured from CCTV showed the gunman carrying what appeared to be an AK-47.

Mr Trump, who is spending the weekend at his golf club in New Jersey, was briefed on the shooting by Attorney-General Bill Barr and Texas Governor Greg Abbott, according to the White House.

Pope Francis on Sunday condemned attacks on "defenceless people" after a spate of gun violence in three American states, including the one in El Paso, Texas.

Speaking to thousands of pilgrims and tourists in St Peter's Square for his Sunday message and blessing, Pope Francis said he was spiritually close to the victims, the wounded and the families affected by attacks he said had "bloodied Texas, California and Ohio".

Pope Francis said all three attacks targeted "defenceless people".

He mentioned the Texas shooting as well as another last week at a food festival in California where three people were killed, and a third in Dayton, Ohio, where 10 people were killed early on Sunday. .

Pope Francis, who has in the past criticised the gun manufacturing industry, then led the crowd in reciting a Hail Mary for the victims.

It has been a particularly bad week for gun violence in the US.

Two people died and a police officer was wounded last Tuesday at a Walmart in Mississippi.

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

Mr Beto O'Rourke, a former US congressman for El Paso who is now running for president, cut off his campaigning in the wake of the shooting.

"I'm incredibly saddened and it's very hard to think about this. But I tell you El Paso is the strongest place in the world, this community is going to come together," he said in a speech to supporters.

Ms Elizabeth Warren, a senator who is among the front runners for the Democratic party's presidential nomination, said: "Far too many communities have suffered through tragedies like this already.

"We must act now to end our country's gun violence epidemic," she said.

Another presidential hopeful Cory Booker said the US had "to end this national nightmare".

"Praying for everyone affected by this unspeakable tragedy, and for our country to find the moral courage to take action to end this carnage."

Mr O'Rourke appeared a bit shaken as he appeared at a candidate forum in Las Vegas on Saturday shortly after news of the shooting in his hometown was reported.

He said he had called his wife before taking the stage and said the shooting shatters "any illusion that we have that progress is inevitable" on tackling gun violence.

The Democrat said he'd heard early reports that the shooter might have had a military-style weapon, saying we need to "keep that (expletive) on the battlefield and do not bring it into our communities".

"We have to find some reason for optimism and hope or else we consign ourselves to a future where nearly 40,000 people are year will lose their lives to gun violence, and I cannot accept that," Mr O'Rourke said.