The survey records the number of guests staying in hotels, motels, backpacker accommodation, and holiday parks in New Zealand each month. Each guest night is equivalent to one guest spending one night at an establishment.
Hawke's Bay Tourism general manager Annie Dundas said it was the biggest May for accommodation in 10 years.
"We've seen really strong growth for some time now," she said. "There was good weather in May, which draws a lot of people.
"North Islanders in particular like to travel when it's warm.
"We're also out of the recession now so people are travelling more, and there's more events."
Hawke's Bay Hospitality Association president Adam Greer said the region's councils and tourism agencies could be credited for the growth.
"Napier City Council in particular have been very proactive in providing good options for people to visit. Developments on Marine Parade and big events are all very positive steps in creating Napier as a hub for people to visit."
Domestic tourism was evidently growing, he said. "More and more families are coming, which is great."
Nationally, guest nights were up 5.5 per cent year-on-year.
As in the previous three months, most of the rise for May was from international guest nights, which were up by 11 per cent. Domestic guest nights were up 5.2 per cent.
Motel Association of New Zealand chief executive Michael Baines said the figures reflected a strong year for tourism so far.
"We've had an awful lot of Aussies coming, and the economic recovery in Europe has brought back the English market that disappeared for a while," he said.
"There's also good and strong continual growth out of the United States and year-on-year growth from China."
Domestic tourism was also positive, he said.
"No one should underestimate the power of domestic tourists."
The recent bad weather around the country hadn't been too disruptive, he said.
"Bad weather does impact on commercial travellers because it can mean they just don't go, but I don't think this winter is any quieter than normal. I'd say it's about the same or better than last year," he said.