Country singer Ingrid Andress has apologised and admitted being drunk while performing a much-derided rendition of the US national anthem, at a baseball stadium.

Andress's erratic performance of The Star-Spangled Banner was widely shared after Major League Baseball's Home Run Derby, in Texas, on Monday.

"I was drunk last night," wrote Andress, who has previously received four Grammy Award nominations.

"I'm checking myself into a facility today to get the help I need. That was not me last night. I apologize to MLB, all the fans, and this country I love so much for that rendition."

She added: "I'll let y'all know how rehab is - I hear it's super fun."

Andress's a-capella version of the anthem was called "painful" and "one of the worst national-anthem renditions ever", on social media.

The Daily Beast headline said: "America unites over new all-time worst national-anthem performance."

Some people posted clips of Philadelphia Phillies third baseman Alec Bohm apparently smirking as Andress was singing.

But she also received sympathy and support following her apology.

"I’m so sorry you’re going through this," singer and actress Lucy Hale wrote. Sending you a lot of my thoughts. Take care of you and you’re going to come out of this so much stronger."

Country star Martina McBride said: "Sending lots of love and positivity. You got this."

Singer-songwriter Julia Michaels said: "Love you, girl. I’m sorry you’re going through this. And I’m sorry the world can be so cruel. Here for you XX."

Fellow singer-songwriter Carly Pearce said: "Being this open takes a lot. You’ve got this. Hang in there."

And one fan posted a video of Andress on stage at a concert, to show her "true talent".

Andress appeared as an a-cappella singer on NBC series The Sing-Off, in 2010 - and after forging a solo career, was nominated for the 2021 Grammy Award for Best New Artist.

She also co-wrote Charli XCX’s hit song Boys and Bebe Rexha’s Girl in the Mirror.