At least 22 people are dead and 59 wounded in what appears to be a terrorist attack on a concert hall in the English city of Manchester.

The bombing took place Monday evening as people began leaving a concert given by U.S. singer Ariana Grande.

Prime Minster Theresa May called the attack “sickening.”

“All acts of terrorism are cowardly … but this attack stands out for its appalling sickening cowardice, deliberately targeting innocent, defenseless children and young people who should have been enjoying one of the most memorable nights of their lives,” May said.

Police said they have arrested a 23-year-old man in connection with the attack.

“Broken,” Grande, 23, tweeted to her fans. “From the bottom of my heart, I am sorry. I don't have words.”

A concert-goer described the scene to the BBC: “She finished her last song … and we heard like a really basey bang, and all I can remember is just everyone … was just running out. People were covered in blood. Some people were having a fight. It was quite scary.”