Rio Tinto has struck a deal with a power supplier to keep New Zealand's Southland aluminium smelter in business for another four years, as recovering commodity prices bolster the chances of survival for the four struggling smelters on Australia's eastern seaboard.

The rescue agreement comes as Rio continues talks over rescue packages for its Australian smelters, and as Alcoa prepares to update investors next week on talks with state and federal governments over a support package and "repowering" plan for its Portland smelter in Victoria.