Former Prime Minister Sir John Key says the fire at SkyCity's new convention centre is tragic.

More than 100 firefighters have used at least 16 million litres of water in an effort to extinguish the blaze, which broke out yesterday afternoon.

Sir John says he doesn't know the extent of the damage - but he told Heather du Plessis-Allan it will be hard to see the convention centre being used for the APEC meeting in 2021.

"What is a great tragedy is that this was going to be the centre point in the showcase for APEC, when you get 21 countries from around the world come to New Zealand and the convention centre would have been on display for the rest of the world to see."

He says that his Government's viewpoint at the time was that the city and country needed a convention centre, but they did not think it was a burden for the taxpayer. 

Giving the project to SkyCity was contentious at the time, but Sir John does not think that is still the case. 

"The demand is absolutely there. The initiative is the right thing."