Watch: U2 have been spotted on Auckland's One Tree Hill.

Watch: U2 have been spotted on Auckland's One Tree Hill. Credit: Newshub

U2 have been spotted at One Tree Hill in Auckland ahead of their two Auckland shows at Mt Smart Stadium this week.

The Irish band visited the One Tree Hill memorial to pay tribute to their former roadie and close friend, Greg Carroll, a young Māori man from Whanganui who charmed the hitmakers in 1984 during the band's first New Zealand visit.

Carroll developed a friendship with U2's lead singer, Bono, working as a roadie and later as Bono's personal assistant. He was killed in a motorcycle accident in Dublin, Ireland, in 1986. He was just 26 years old.

U2's 1987 song, 'One Tree Hill', was written by Bono in Carroll's memory, the tribute featuring as the fifth single on the iconic The Joshua Tree album.