The company said that as well as redundancy packages, affected staff had been offered a support programme to assist them "through the transition ahead".
Staff had been given the opportunity to apply for roles in Sanitarium's Auckland facility and positions at its sister firm in Australia, van Heerden said.
Sanitarium said its intention was to get Marmite production at the Christchurch plant up-and-running as soon as possible, and the site would continue to function as a distribution centre.
It would be at least 18 to 24 months before the company could manufacture Weet-Bix at the Christchurch site, van Heerden said.
In the meantime, he said the company would continue to transport Weet-Bix to the South Island from Auckland, as well as Sanitarium factories in Australia.
Van Heerden said that although staff had been expecting the news of the closure, it still came as a shock.
"They've had severe issues in their personal lives [as a result of the quakes] and then they get this at work," he said.
"The majority" of the 36 staff offered redundancy packages were expected to take the offer up, he said.
Van Heerden said no decision had been made on the long-term future of Weet-Bix manufacturing in Christchurch.