Registered property deals jumped 21.71 per cent to 12,071 last month from April, the highest monthly figure recorded so far this year.
Centaline Property Agency said the total value of the trades was $32.3 billion, up 14.93 per cent from April.
Centaline's unofficial figures better reflect market activity in April because of the normal time lag of about four weeks between property purchases and registration.
The Land Registry has yet to release official figures.
Centaline said registrations of first-hand property deals below $20 million, excluding registrations of car-parking spaces, climbed 22.9 per cent to 4,750 deals last month, while the value of such deals rose 29.53 per cent to $15.6 billion.
In the secondary market, Centaline said there were 6,403 deals below $20 million registered last month, up 17 per cent from April.
Registered property deals worth below $1 million increased 25 per cent to 1,364. There were 1,069 sale-and-purchase agreements for properties valued between $2 million and $3 million registered, up 23 per cent from April.