London's Gherkin skyscraper has been put up for sale, with interest expected from Chinese, other Asian, and US buyers, estate agency Savills has said.
The City of London tower is expected to fetch offers in the region of £650m, the firm said.
Savills and Deloitte Real Estate have been jointly instructed to sell 30 St Mary Axe, which is the building's formal title.
The skyscraper was placed in receivership in April.
The estate agents have begun marketing the building, with adverts placed in the specialist press, and a website for investors to register an interest, Stephen Down from Savills told the BBC.
"We've started the ball rolling," he said.
Interest is expected from Chinese, Hong Kong, Singaporean and North American investors, among others, he said.
"I suspect there will be an iconic element to this [sale]," Mr Down added.
After a vetting process on both sides, either one party will be selected, or a number of sealed bids will be accepted, by the end of September or the beginning of October, he said.
"We could see offers in excess of £650m," he added.
The tower was placed in receivership in April by its creditors after one of its owners was placed in insolvency.
Germany's IVG Immobilien, which co-owned the building with private equity firm Evans Randall, filed for insolvency last year.
Although Evans Randall said it was willing to buy a bigger stake in the tower, it was unable to agree a new ownership plan with IVG.
Deloitte was appointed a receiver in April of the 40-storey building.
The skyscraper, which was designed by Lord Foster, opened in 2004. It is currently let to around 20 tenants, including Swiss Re.