Twenty people have been killed and 26 injured in a mass shooting at a Walmart store in the Texas city of El Paso.
Governor Greg Abbott described it as “one of the most deadly days in the history of Texas”.
Police are investigating whether the attack, which happened a few miles from the US-Mexico border, was a hate crime.
A 21-year-old man is in custody. Police said the suspect lived in Allen, Dallas, about 650 miles (1,046km) east of El Paso.
He has been named by US media as Patrick Crusius.
CCTV images said to be of the gunman and broadcast on US media show a man in a dark T-shirt wearing ear protectors and brandishing an assault-style rifle.