"As soon as pre-orders were available, we were inundated with phone calls from customers and traffic overload brought the booking server down one time," a spokesman at Hyundai said.

Some 733 pre-orders for Hyundai's hydrogen fuel cell SUV Nexo were made on the first day of sales, the carmaker said on Tuesday.

The sales were far beyond the expectations and three times higher than those eligible for the government subsidy given to buyers of electric vehicles -- 240 for this year.

It was also unexpected that the pre-orders were mostly made by individual customers, because electric vehicles are typically sold to local governments as they are provided with a subsidy for their purchase in line with the government-led efforts to boost sales of electric vehicles.

The Nexo can drive up to 609 km with just one charge, though the availability of charging facilities is still limited.

With subsidies, customers can buy the SUV with a price tag between W33.9 million and W37.2 million. This is similar to the price of Hyundai's midsize SUV Santa Fe, which sells between W28.95 million and W36.8 million.