Tesla said Wednesday its 2015 sales were up 51 percent as the electric carmaker reaffirmed plans for its new model that aims at a wider market.

The California company led by Internet entrepreneur Elon Musk said it sold 25,202 Model S vehicles in the year, up from 16,689 in 2014.

Tesla, which is investing heavily in new vehicles and battery technology to drive the market for electric cars, reported a fourth quarter loss of $320 million on revenue of $1.2 billion.

The company said its Model 3 -- with an estimated price of $35,000 or around half that of its best-selling car -- would be unveiled on March 31, with production and deliveries to start in late 2017.

A shareholder letter said the company is seeing "growing worldwide demand for Tesla vehicles, supported by record production," and that deliveries rose by more than 50 percent in the fourth quarter from the prior three-month period.

"For 2016, we are planning for even faster delivery growth than last year," the letter said.

While Tesla has only a small slice of the luxury car market, it has a loyal user base and strong demand that is impacting the industry.

As other carmakers rush to put electric vehicles into production, Tesla is growing its share at the high end of the market while preparing for a more affordable Model 3.

In the fourth quarter, "we increased global deliveries over 76 percent year-on-year as Model S market share gains continued in every geographic region," the letter said.

"In the US, just over three years after entering the market, Model S took share from all incumbent manufacturers to become the number one selling comparably priced four-door sedan. In fact, Model S was the only vehicle in its class with growing sales last year."

Tesla in the past quarter sold just 206 of its newest vehicle, the Model X, which includes "falcon wing doors" and a panoramic windshield, with a price starting at $130,000.

But it anticipates a Model X production rate of 1,000 vehicles a week in the second quarter of the year.

Tesla said it expects to deliver 80,000 to 90,000 Model S and Model X vehicles in 2016, with the more expensive version getting a bigger share as the year goes on.

"Achieving these results in 2016 should leave us well positioned for 2017, when we plan to launch Model 3 and take another significant step towards our mission of accelerating the world's transition to sustainable transportation," said the letter from Musk and chief financial officer Jason Wheeler.