Saved from the chainsaw

Not a perfect shot but I'm hoping there's enough information in it to allow cabbagetree or another NZ horticultural blipper - to identify this tree or shrub?

It looked pretty boring in my garden until it - quite suddenly - burst into flower. The flowers resemble hibiscus but are small (about 40mm across) and the tree (or shrub) is about twelve five metres high with thick deep green leaves.

This one was on my list for the chainsaw until it revealed its hidden charm.

Update: identified by cabbagtree as a Norfolk Island Hibiscus (lagunaria patersonii). Thank you ;-)