Mayor Hamish McDouall says Whanganui District Council will work hard with Mars Petcare and Whanganui & Partners to give the 152 affected workers options in the future.
Mars confirmed this weekthe plant will close at the end of next year.
"My sympathies go out to those who have got an unsettled time in front of them," McDouall said.
"What's good is there is quite a long lead time which will allow many of the Mars associates to find alternative employment which is great.
"I've made it clear to Mars that my expectation is that every employee will be either retired, in employment or in training at the end of next year.
"That's what success would look like."
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McDouall said he thought many of the workers would be absorbed into other employment, and that big companies had already enquired about employment opportunities.
"Had this announcement happened five or six years ago, it would've been a real economic gut-punch for Whanganui but now I think we're more resilient, we're more buoyant and there are companies craving the type of good quality worker they have at Mars."
Manufacturing and Construction Workers' Union general secretary George Larkins said no definite date had been given and closure could take longer as equipment was moved to a new factory in Thailand.
The company announced in late September that it intended to move production of cat food pouches from Castlecliff to a facility in Thailand, and said it was going through a consultation process with staff.
One of their suggestions has been to use the factory solely to produce petfood for New Zealand, but Mars has said that is not financially viable.
Staff, who were devastated by the closure, had done their utmost to keep the plant going, Larkins said. They had known for years that the factory was inefficient, and many agreed to work flexible hours so production could stop at times when it was unprofitable.
Mars had been a reasonable employer, Larkins said, with people paid a living wage soon after starting jobs.
Mars supply transformation manager Dan Pope said moving the plant to Thailand would save Mars US$10.8 million a year,
The Thai factory would be bigger and closer to the growing India and Southeast Asia markets, whereas the New Zealand and Austrialia market was declining.
Because of that huge saving, Larkins intends to ask for as many benefits as possible to staff in their last year of service. Bargaining for their collective agreement starts later this month.
He wants a wage increase of more than three per cent for them, and certainty that all of their service will be recognised in redundancy packages.
The redundancy packages in their agreement are fairly good, he said. Staff get six weeks' pay for the first year they have worked, and another two weeks for each year after that - to a maximum of 46 weeks.
He also wants people who get new jobs and leave before the end of 2020 to get whatever redundancy they would be entitled to, though they will not have been officially made redundant.
If a lot go before the factory closes, Mars should hire casuals or people on fixed terms to fill the gaps, he said.
The total cost of running the factory in Whanganui is US$11 million a year, with US$7.8 million of that wages.
Whanganui and Partners chief executive Mark Ward said the agency would work as a facilitator to bring businesses to the site now the closure had been confirmed.
"Examples like the Mill Road development show the ongoing demand for these kinds of businesses basing themselves in Whanganui," Ward said.
"We're seeing growth in all our economic indicators: GDP, consumer spending, population. We are on a clear upward trend, which is attractive to investment.
"Interest rates are also at record lows, making now the ideal time for businesses to spend on land, plant, technology and facilities.
"It's the right time, right place, we just need to find the right businesses or investors to take up the opportunity."
Whanganui Chamber of Commerce chief executive Sue Stuart said the economic decision was challenging in corporate terms, and would be challenging for staff and suppliers that worked with Mars.
"The chamber will be reacting to this positively and will be collaborating with other organisations to turn the situation into an opportunity by involving local businesses to assist where possible."
Stuart said Whanganui had a strong social and business community that was very supportive.
"Given the time frame, there will be time for staff to seek other opportunities and find alternative employment and suppliers alternative business.
"Whanganui has experienced this before and is a resilient community. We are optimistic that morale will, over a long term, be boosted by all the support offered."
In a statement, Mars Petcare said it would now work with staff to develop a support programme to help them transition to new jobs.
It said staff who left Mars Petcare when production ceased in late 2020 would receive redundancy compensation, as well as training to meet local demand, outplacement assistance and financial planning.
The company owns the Castlecliff land on which the factory stands and said it would work with community and business leaders to identify options for future sale and use of the property.