Police officers at the site of the shooting outside the Walmart store in El Paso, Texas

US President Donald Trump condemned Saturday's mass shooting at a Walmart store in Texas as an act of cowardice, saying there could be no justification for the killing of innocent people.

"Today's shooting in El Paso, Texas was not only tragic, it was an act of cowardice," Trump wrote on Twitter.

"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."