The corpse flower at the Dunedin Botanic Garden is opening and beginning to unleash the first whiff of its fearsome scent.

The rare event started when the flower began to open about noon today, and the smell is expected to get worse - much worse.

Famous for producing one of the world's largest flowers and a nauseating smell, comparable to rotting flesh, the flower is expected to draw large crowds.

The bloom is pungent but short-lived, lasting just 24 to 36 hours, so the winter garden glasshouse opening hours have been extended to allow people to have a look.

Dunedin City Council botanic garden team leader Alan Matchett confirmed when contacted this afternoon the flower was opening, but was "obviously not fully open yet''.

"It's starting to give a little bit of an odour.''

It is the first time the plant (Amorphophallus titanium) had flowered in the decade it had been at the garden.

The winter garden glasshouse, which holds the odourous beast, is open unitl 8:30pm Saturday and on Sunday from 9am to 8:30pm.