One man has died and two others are injured after a shooting incident at a hotel in Dublin.

The attack happened while a boxing tournament weigh-in was going on at the Regency Hotel on Swords Road, around three kilometres north of the city centre.

There men aged in their 20s or 30s were injured in the shooting.

Gardai said one of the men has since been pronounced dead.

They were called along with paramedics to the scene at around 2.30pm on Friday afternoon.

The two other victims have been rushed to The Mater and Beaumont hospitals with what are suspected to be gunshot wounds.

The scene has been sealed off.

The weigh-in was ahead of a Clash of the Clans boxing bout at the National Stadium in the south of the city, scheduled to take place on Saturday evening.

The event included a WBO European lightweight title fight between Jamie Kavanagh and Antonio Jao Bento.

Box Nation, the television channel scheduled to broadcast the fight, said in a message on Twitter that the show had been cancelled due to the shooting.

"Following today's incident at the Dublin weigh in, tomorrow's show from the National Stadium has been cancelled," the post said.

The bout was being promoted by Frank Warren and MGM Promotions, according to MGM, a Marbella-based gym run by Birmingham-born Irish boxer Matthew Macklin.

Two years ago, former European light-middleweight boxing champion Jamie Moore was shot twice in the legs in Marbella, where he was training Macklin at the time.

Witness Mel Christle, president of the Boxing Union of Ireland, was standing on a podium where the last of the boxers weighing in had just stood down when he heard gunfire erupting outside the room.

"There was a horrific cracking noise, in front of me, out of the banquet room - it was a place called the Regency Suite," he said.

"There was an incredible noise out there, and that is where I saw a body, a corpse, lying literally at the edge of the reception desk.

"So I'm sure he (the victim) was trapped - he was riddled."

Mr Christle said one of the gunmen was dressed up as a woman and aged in his early 20s.

The boxing chief was adamant the attackers were not targeting the boxers gathered for the weigh-in, but other individuals who were hit in the hotel reception.

He said there was panic as some people dived for cover when they realised what was happening.

"I actually saw the sheer fear that will live with them for a long, long time," he said of those who witnessed the shooting.

"It actually touched me, how afraid - I'm sure adults were afraid, but my God, the children couldn't believe what was going on."

Mr Christle said he saw two attackers wielding handguns - one dressed as a woman - but others saw a further pair of accomplices dressed in garda-style uniforms.

Amateur video footage of the boxing weigh-in at the time the gunfire started has been posted online, showing scenes of frenzy and terror as men, women and children scatter in fear of their lives.

One child is heard crying: "Daddy, help me. Daddy, what was that?"

Amid the pandemonium a woman is heard saying: "What the f*** is going on?"

Up to 300 people were attending the weigh-in at the time.