US presidential hopeful Beto O'Rourke has coined a controversial new campaign slogan in the wake of the Texas shooting that left seven dead and 22 injured.

Key points: Beto O'Rourke tweeted the phrase "this is f***ed up" and then repeated it on CNN after the Texas shooting

Beto O'Rourke tweeted the phrase "this is f***ed up" and then repeated it on CNN after the Texas shooting While some criticised the poor language, his campaign defended it and began selling t-shirts

While some criticised the poor language, his campaign defended it and began selling t-shirts The gunman has been identified as 36-year-old Seth Aaron Ator

After addressing a crowd in the immediate aftermath of the shooting on Saturday, the Democratic candidate tweeted: "We don't know how many have been killed. We don't know the motivation. But here's what we do know: This is f***ed up."

While some responded negatively to his choice of words, Mr O'Rouke doubled down on CNN the day after the shooting.

"We're averaging about 300 mass shootings a year. No other country comes close, so yes, this is f***ed up," he said.

"If we don't call it out for what it is, if we're not able to speak clearly, if we're not able to act decisively, then we'll continue to have this kind of bloodshed in America, and I cannot accept that."

Beto O'Rourke has been an outspoken critic of US gun laws. ( AP: Charlie Neibergall )

The recurring phrase has now even launched a line of merchandise, created by Mr O'Rourke's campaign.

T-shirts featuring "This is f***ed up" and "End gun violence now" are being advertised on Mr O'Rourke's official website, with all proceeds going to gun control charities.

The proceeds from sales of the shirt will go to pro-gun control charities. ( Twitter: Team Beto )

Some have reacted badly to the use of language, questioning whether swearing reflects poorly on Mr O'Rourke or undercuts his message.

But Mr O'Rourke and his team have not wavered.

Loading

Loading

Authorities have identified the Texas shooter as Seth Aaron Ator, 36, of Odessa.

Online court records show Ator was arrested in 2001 for a misdemeanour offence that would not have prevented him from legally purchasing firearms in Texas, although authorities have not said where he got his weapon.

Ator acted alone, and federal investigators believe the shooter had no ties to any domestic or international terrorism group, FBI special agent Christopher Combs said.

Hundreds of people gathered at a local university on Sunday night for a prayer vigil.

ABC/AP