UPDATED 4.15pm: Some 850 firefighters have reached for the sky today - climbing to the top of Auckland's Sky Tower for an annual challenge.

Mt Wellington's Josh Harrison came out on top, conquering the more than 1,100 stairs in just eight minutes and 46 seconds.

The challenge raises funds for Leukaemia and Blood Cancer New Zealand.

General manager of the charity Georgie Hackett said the event's like a carnival at the bottom of the Tower, but for those bursting through the doors of the stairwell at the top, the scene's a bit different.

"Elated, but exhausted. It's huge to get up those stairs. So, there's a bit of a recovery area, but people have the biggest smile on their faces. What an amazing achievement to climb up 1,103 stairs."

Some of the competitors travelled from as far afield as the USA, Australia, Germany and Chile to take part.

Each participant had to wear full kits and breathing apparatus, weighing up to 25 kgs.

Hackett said the event's taken a lot of hard work, both with fundraising and training.

"People around the country have just been so generous, and these firemen and firewomen have just put in hours and hours and hours of fundraising, in tiny, tiny communities right across the country."

Hackett said everyone has dug extra deep this year.

"We've reached a new record for the event fundraising wise, so we're about to hit one-point-one million dollars, which is just absolutely incredible."