The council voted (10-1) on Tuesday night to buy 39 Edgar Street for $820,000 after being approached by the owner about a sale last year.

The purchase adds to 24 properties council owns in the block bordered by Edgar, Herbet and Maude streets north of Belmont Citi Centre.

In a report prepared for councillors, the property was described as "critical" to "long term" plans for a "central precinct" in Belmont.

The council has been buying properties in the block, zoned B2 Business Centre, since the mid-1980s.

Cr Kevin Baker, who was the only councillor opposed to the purchase, questioned why the council was buying up land without having a master plan for the area.

"If we were looking at doing this in the mid-80s, how serious are we about this?" he said.

"We are in extraordinary times ... I don't think it is appropriate use of public money. $820,000 is a significant amount of money."

Cr Barney Langford asked for a "brief rationale" on the plan's history, with property development manager David Antcliff saying the "the focus" was for "expansion of the Belmont economic centre".

"A master plan process is starting at the moment and we're considering what that modern economic centre would look like in an expanded space," he said.

It is not clear how many properties the council wants to acquire, but a map of those it already owns suggests at least four more would be needed to redevelop the block west of, and including, the Herbet Street car park.

Mayor Kay Fraser briefly spoke on the matter, saying Belmont had "huge potential" and it was "important we plan for the future".

The property will be purchased with funds from the strategic property reserve and leased to generate yields of 7.0 to 7.5 per cent per annum until it is needed.