A $600 million metals processing plant has officially opened at Port Pirie, securing more than 700 jobs.

Plant operator Nyrstar said the facility would significantly improve air quality in the town by reducing lead-in-air emissions by a margin unachievable with the old smelter at the site.

Premier Jay Weatherill opened the plant along with Nyrstar executives, and said it marked a new chapter in the history of Port Pirie.

"For Nyrstar, improved efficiencies provide a pathway to uplift earnings, and for Port Pirie we can lock in better health and environment outcomes for decades to come," he said.

Nyrstar chief executive Hilmar Rode said the development was crucial to the company's future, and it would put the safety of the community first.

"We are totally committed to a successful and safe ground plant," he said.

"We will face many more challenges along this journey, but I'm confident if we all continue with the same dedication that we have seen … we will ensure a sustainable future for the Port Pirie smelter and for the broader community."

Premier Jay Weatherill and Regional Development Minister Geoff Brock at the ceremony. ( ABC News: Glen Moret )

Regional Development Minister Geoff Brock welcomed Nyrstar's investment in the area.

The redevelopment also was underwritten by the State Government by $291 million.

"Across Port Pirie, economic and social investments are being made that would not have been possible without Nyrstar committing to its long-term presence in this community," he said.

"Air quality is also expected to improve during the two-year ramp-up toward full production at the new facility, and will accelerate once the old sinter plant is decommissioned."

Smelter has chequered past with air pollution

Monitoring lead levels in the blood of people who live in the town will continue.

Regular checks have noted improvement in the amount of lead in those in the area, but the problems remain.

The plant is expected to be working at full capacity within two years.