The maker of Lindor chocolate balls is expanding a plant in Stratham, New Hampshire, over the next four years, constructing high-tech production lines for premium chocolate, the company said Tuesday. The site will eventually have more than 1 million square feet of space for production, storage and distribution.

After years of stagnation, the US chocolate market is perking up. Lindt reported a 4% increase in adjusted sales in North America in the first half as it added more displays to advertise its Lindor and Excellence brands in shops. The Kilchberg-based company became the third-largest chocolate maker in the US when it bought Russell Stover in 2014, a purchase that weighed on sales growth as Lindt spent years weeding out less profitable products.

The American chocolate market has been challenging to companies like Nestle SA, which exited the US by selling its confectionery unit there to Ferrero SpA.

Russell Stover’s revenue stabilised to a “modest dip” in the first half, supported by demand for a sugar-free range introduced in late 2017. Lindt said it’s on track to achieve its target of about 5% organic sales growth this year and that first-half operating profit rose 12%, in line with analysts’ estimates.