Whanganui business Axiam Plastics has increased its staff from 90 last year to 140 this year, and taken on some of the workers laid off by Mars Petcare.
The growth has come from some new customers, but also from existing customers wanting more product, general manager Matthew Smith said.
"It's just they have all grown a little bit."
The factory operates six days a week, with three shifts per day.
Axiam Plastics makes plastic parts and components for other products. Some are assembled on-site, but most are sent away to New Zealand customers to assemble.
The parts could be housings for electronic equipment or medical devices. The customers include schools, farms and the New Zealand Defence Force.
The plastic is imported in granules, with much of it from China. Axiam also uses recycled plastic, but not for medical or safety products.
"We regrind the waste that we have here, and put it into new products," Smith said.
"That's a big focus of being environmentally aware."
Sales for the factory dropped off last year during the Covid-19 lockdown, but it had to keep running because it was supplying medical equipment.
Its growth is being recognised with the "significant investment" into a warehouse that will increase the factory's size by 20 per cent. The new building will house bulk material, packaging, dispatch and inwards goods.
Trucks will enter and leave it from London St and product will flow through the site more efficiently, Smith said.
The warehouse is being constructed by Masterbuilt and is the same style as the existing buildings. The build began in early February and is part of a general rearrangement to accommodate growth.
Still to come is a display area for products.
The aim was to stay ahead and be positioned for growth, and Smith said he hoped Axiam Plastics would grow in tandem with nearby Axiam Metals. It makes metal components for some of the same products and shares some staff.
"We're working towards being the 'total solution' type of business," Smith said.