National will contribute another $120 million toward building a new multi-use arena in Christchurch if elected for a fourth term.

The money would be set aside in next year's budget, party leader Bill English announced in the city on Thursday along with Christchurch regeneration spokeswoman Nicky Wagner.

She says the preference is for a 30,000 seat arena with a fully closed roof, though the final decision will come down to the community and Christchurch City Council.

"This isn't just any other stadium, it's a central hub that will be designed to bring together the community and invigorate wider Canterbury," she said.

"The multi-purpose concept is critical because it will ensure the facility is well used and cost effective, with broader opportunities for events."

The project is currently scheduled for 2020, but Ms Wagner said the council would be keen to look at whether they could bring it forward.

Mr English indicated the money would be set aside in next year's budget.

The government has already committed $59 million toward the project and National's commitment on Thursday would be in addition to that.