The destroyed building was not connected to electricity and there were reports of illegal entry.
"We are looking for any information about people who have been dossing down in the building recently," Detective Sergeant Darren Pritchard said.
"We believe the fire was started intentionally and we would like to hear from anyone who knows who was responsible for this."
Police are also seeking witnesses to any suspicious behaviour in the area, opposite Ravensdown fertiliser factory, in the early hours of Sunday.
"There would have been some traffic on the highway at this time of the night, so we are keen to speak to anyone who may have seen something out of the ordinary near the building."
The building had not been used since it was a paua farm.
Mr Govsky said the destroyed building had become an attraction.
"We have probably had about 80 cars in here today, coming in and out the drive looking at everything."
The building was once a nightspot called Cabaret Cabana, which was opened in 1950. In the 1970s, it was called the Polynesian Palace.
Police and fire investigators say anyone with information should contact Mr Pritchard at Hawke's Bay police on 06 831 0700, or anonymous information can be left at Crimestoppers on 0800 555 111.