Paramount Group Inc., an office landlord, raised $2.3 billion in the largest-ever initial public offering for a U.S. real estate investment trust.

Paramount, which plans to qualify as a REIT, is going public as investor demand for property trusts is soaring partly because they offer higher yields than some other securities, such as U.S. Treasury notes. The Bloomberg REIT Index has gained more than 20 percent this year, nearing its highest level since March 2007. Paramount’s offering surpasses Douglas Emmett Inc.’s IPO in 2006, which raised $1.6 billion, including an overallotment, as the biggest in the U.S.