A three storey extension to The Canberra Hospital's emergency department and intensive care unit has been officially opened.

The $7.5 million annexe will provide eight new treatment spaces in the emergency department and seven new beds in the ICU.

The upgrade was jointly funded by the Federal and ACT governments.

Chief Minister Katy Gallagher says staff will move in shortly and it should be fully operational next month.

"It's essentially been fixed on the end of the existing emergency department for good reasons," Ms Gallagher said.

"We don't have a lot of space around that emergency department but this has been I think a very creative way of ensuring that we have got more space to grow into."

Ms Gallagher says in the long term it will help cut waiting times.

"It won't be the only thing that will help but the extra staff that we've employed will allow a new model of care to be implemented," she said.

"It is not the only solution but it will help us see more patients in clinical areas."