Ford, Holden and Toyota and the associated businesses that manufacture car components make up at least 6.4 per cent of Melbourne's 14 million square metres of industrial stock, according to new research by Urbis.

Holden and Toyota control about 41 hectares of property in Port Melbourne; with Toyota owning more land in Altona and Ford occupying further properties in Broadmeadows in the north.

"A lot of the buildings are secondary or tertiary stock and there's not a lot there that will be used by other corporates because there's not a lot of manufacturing around anymore," Urbis director Shane Robb said.

"It will become backfill warehousing until a higher and better use becomes available for the land. The GM Holden land in Port Melbourne has a higher underlying land value and that will be developed first," he said.

Knight Frank agent Matt Croft said "the ripple effect will be significant".

The Urbis report found Melbourne's industrial vacancy rate has fallen to 4.5 per cent from the 5 per cent recorded in August 2014, and the 5.6 per cent posted 12 months ago.

Low interest rates are driving the declining vacancy rate, with owner occupiers buying secondary and tertiary stock and getting out of the rental market.

The vacancy rate in this segment dropped to 3.5 per cent from 4.7 per cent last August, whereas the vacancy for A-grade stock remained steady at 5.4 per cent.

"That's the most surprising aspect of the report. The properties in the A-grade market, where developers build new buildings for tenants, don't take a long time. Most of the development groups have more land and they just develop the next wave of stock," Mr Robb said.

This is expected to be a bumper year with around 500,000 square metres worth of new buildings under construction, including a 70,000 square metre building for Toll and a 40,000 square metre facility for TNT, both at Melbourne Airport. Mainfreight also has a 40,000 square metre building earmarked for a site in Epping.

Mr Croft warned that "there's still a lot of land but the tenant pool is tightening".

Mr Robb noted that some businesses, mostly privates, are buying older buildings "at well below replacement cost because of the low interest environment", he said.

Last October, the privately owned ARB Corporation paid $19 million to buy back the Kilsyth headquarters it sold to Growthpoint in 2005 for $16 million.

Another private company paid $14.5 million to Centuria last December for a five-hectare industrial property at 28 Salta Drive in North Altona.

The highest vacancy rate, of 6.9 per cent, was recorded in the north, where two vacant buildings make up half the number.

A 46,000 square metre building previously occupied by Jan Cameron's Retail Adventures is empty at Tullamarine, and a 39,000 square metre climate-controlled warehouse at Somerton has been vacated by Mars.