Fewer tablet computers were sold around the world in the first three months of 2014 than in the same period a year earlier, the first time in history that's happened, a market research firm said Wednesday.

NPD DisplaySearch said 56 million tablets were sold worldwide between January and March, down from about 59 million last year.

NPD still expects 285 million tablet computers to be sold worldwide this year, an increase from 250 million last year. But the sector started out the year at a slower pace because of delayed launches of new devices and declining demand for smaller, seven-inch tablets in the Asian market, which is increasingly buying large smartphones instead.

Originally, NPD was forecasting tablet sales to jump to 315 million this year, before revising that estimate downward on Wednesday.

After exploding out of the gate with the launch of the iPad in 2010, tablet sales have grown exponentially. But that growth is now slowing as the market evolves. Growth is expected to increase by only 17 per cent this year, and decline to single digits by 2017 and beyond, NPD says.

There's still more tablets sold every year than all other forms of mobile computing combined — a category that does not include smartphones. That trend is not expected to change anytime soon. But smartphones with larger and larger screens are also eating into tablet demand, though not enough to knock tablets off their dominant perch, NPD says.

"There is a risk that the replacement cycle for tablet PCs will lengthen beyond the one-to-two-year range unless brands can develop more attractive usage scenarios," NPD analyst Hisakazu Torii said in a statement