An Irishman was seriously injured on Saturday after participating in the famous Running of the Bulls festival held every year in Pamplona, northern Spain.

Robert Thackberry, 28, was one of more than 20 people who were trampled in a crush at the narrow entrance to the ring as the six-half ton bulls they were trying to run from attempted to climb over them from behind.

Thackaberry, an engineer from Dublin, was with 18 friends from Dublin and Scotland who arrived for a stag weekend at the running of the bulls.

Hsis friend Rob Smyth told Independent.ie: "We all got back to the a cafe after the bull run thankful we had escaped with our lives but Robert wasn’t with us. Then we saw the repeated TV footage of him being brought out from the crush. He was blue.”

Thackaberry was knocked out, severely bruised and had a huge gash on his nose.

Runners were trampled on in a massive crush at the entrance to the bull ring as the animals they were trying to escape from tried to climb over them from behind.

Thackaberry was initially described as “serious” with asphyxia caused by crush injuries to his chest.

He was named only by his initials “R.T” because it was feared his condition was so serious.

“That’s where we saw the highlights - and feared the worst,” said Rob.

Of the 23 people injured, a 19-year-old Spaniard is said to be suffering from "very serious" injuries of acute asphyxia caused by crush injuries to the chest, the Irish Independent reports. Two of the injured suffered gore-related injuries.

The Running of the Bulls was made famous by Ernest Hemingway in his 1926 novel 'The Sun Also Rises.' The annual festival, held July 6-14, is the largest in Spain and attracts many foreigners.