"The strong result is mirrored in the comments from respondents, which were over 58 per cent positive - the highest this year," Beard said.
She said the positivity highlighted an improving building/construction sector, increasing offshore orders and new customers/opportunities for their business.
"The mood of the sector is typified by one respondent noting that after five years they now feel confident enough to hire extra staff."
All five main indices expanded in May. Deliveries measured 54.6 and finished stocks recorded 51.8.
Canterbury was the strongest region, reaching a five-year high of 67.0. Northland also showed a strong upswing in activity, measuring 60.5, and the Otago/Southland region bounced back from recent declines to 60.7. The Central region dipped from April to 55.4.
BNZ Economist Doug Steel said the PMI results puts upside risk to the country's manufacturing and overall economic growth forecasts.
"The strong result essentially gives us more confidence that the recent and forecast upswing in construction activity will flow through to manufacturing activity, with the usual lag."