Clarifications to a Trump administration initiative that offers shelter from capital gains taxes in exchange for investment in designated geographic areas has energized a growing list of city investors seeking to take advantage of the program.

Chief among the rules that were articulated Wednesday for so-called opportunity zones was a more detailed description of the types of businesses that qualify for investment. Those that have employees who work in or are managed from facilities in an opportunity zone are eligible, clearing up questions about how much of a business's operations must be conducted within a zone to qualify for the incentives.

"We now have the confidence to fund a business and know they won't be in violation of the opportunity zone rules," said Brian Phillips, an investor who plans to raise $25 million to back startups in the designated areas, including the Brooklyn Navy Yard. "It's accelerating the start of our fund."

Real estate investors also will benefit from additional leeway. Several large funds are planned by major landlords including RXR Realty, Normandy Real Estate Partners and Silverstein Properties, to buy up portfolios of office and residential buildings within the city's 306 designated zones. The program allows investors a 15% discount on reinvested capital gains and exempts any further taxes on proceeds reaped from investments within a zone, so long as the money stays invested for 10 years.

That time requirement sparked fears of restrictions on when assets could be bought or sold, but the updated guidelines make clear that fund managers can make trades so long as investors keep their money locked into the investment vehicle for the required period.

"These funds are going to have multiple properties," said Marty Burger, CEO of Silverstein Properties, which is raising an opportunity zone fund in partnership with Cantor Fitzgerald that could top $1 billion. "As long as the money stays in the fund and is not distributed, it counts. That's a huge clarification."

There are more than 300 opportunity zones in the city, in mostly low- income areas in need of investment. Experts on the program say there is about $6 trillion on the hook for capital gains in the country that could seek shelter in opportunity zone investments.