Promising rugby union player Nevin Spence died alongside his father and brother late Saturday after they fell into a slurry tank at their farm in Northern Ireland.

Spence, 22, rose to prominence playing for Ulster Rugby and was a rising star on the cusp of Ireland's international team.

The Northern Ireland Ambulance Service (NIAS) said his sister was taken to hospital after she inhaled fumes during the accident at the family farm in Hillsborough, County Down, to the east of the British province.

"Three were unconscious and NIAS paramedics commenced resuscitation efforts immediately assisted by other ambulance personnel," the service said in a statement.

"One of the four showed initial signs of responding to the efforts of the crews and was transported immediately to the nearby Lagan Valley Hospital, where unfortunately he died a short time later.

"Despite the best efforts of all involved the other two men died at the scene.

"A female was treated at the scene and taken to the Royal Victoria Hospital where she is recovering from the effects of fume inhalation."

Rugby players and fans paid tribute to Spence, who was part of the Ulster Rugby squad that reached the European Cup final last season, and was predicted to have a bright international career ahead of him.

"Deeply saddened to hear of the tragedy in Hillsborough this evening," Northern Ireland First Minister Peter Robinson said in a message posted on his Twitter page.

"My thoughts and prayers are with family at this time of devastation."

Slurry, a combination of manure and water, is stored in tanks at many farms until it is ready to be applied to the land as fertiliser.