The last worker returned to the surface on Tuesday evening, some 18 hours after the fire started at the Rocanville, Saskatchewan, mine early that morning.

There were no injuries, the world's biggest producer of the crop nutrient potash said in a statement.

The plant, which has annual operating capacity of 2.7 million metric tonnes (2.97 million tons), normally runs 24 hours a day, seven days a week.

It had been operating at normal speed prior to the fire, Potash Corp spokesman Bill Johnson said on Wednesday morning.

North American potash inventories were one-third larger than the five-year average in August at the producer level, highlighting reduced demand from key buyer India.

Potash Corp is whittling down its stockpile by shutting down its biggest mine, at Lanigan, Saskatchewan for nearly a month until mid-October.

The Rocanville fire started with a wooden spool of cable in the mine. Twenty-nine workers were underground at the time. Nine were rescued on Tuesday morning, but the remaining 20 were trapped in underground rescue stations until the last worker was recovered Tuesday evening.

Potash Corp shares were flat in early trading in New York and Toronto.

(Reporting by Rod Nickel in Winnipeg, Manitoba; Editing by Gerald E. McCormick)