One of the East Coast’s big real-estate investors is launching a West Coast affiliate with local partners with plans to build apartments in cities like Seattle, Portland and Los Angeles.

New York-based Mack Real Estate Group announced today it had invested in Mack Urban, a Los Angeles real-estate firm that combines the portfolios of Seattle’s Harbor Urban and Los Angeles’ Urban Partners.

The new partnership plans to build about 3,000 apartments over the next five years in the Pacific Northwest, focusing on urban centers like Seattle and Portland, said Richard Mack, CEO of Mack Real Estate Group.

Mack said he and his father, William Mack, recently left AREA Property Partners, the international real-estate fund manager they founded in 1993, in order to focus on buying and holding real estate for the long term.

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With the Macks’ backing, the local unit can pursue projects that might take longer to bring to fruition than would be acceptable to most institutional investors, said Mack Urban president Matthew Burton.

Seattle’s Harbor Steps is the best illustration of that approach, said Jim Atkins, managing director of Harbor Urban. The predecessor to Harbor Urban developed the downtown Harbor Steps complex from 1992 to 2000, helping reinvigorate a once seedy neighborhood.

A more recent example: Harbor Urban this week said it has signed a long-term lease on a parking lot between Alaskan Way and Western Avenue on the north side of University Street. The firm is considering a residential or hotel project.

“It’s a civic investment with the opportunity to build a legacy project that becomes part of the new Seattle waterfront,” Atkins said in an e-mail, adding that the site is “just a few blocks north of Harbor Steps where it all began.”

Harbor Urban and Urban Partners already have more than 3,500 apartment units in Seattle, Portland and Los Angeles in the pipeline or in lease-up, officials said.

Paul Keller, CEO of Mack Urban, said the company will seek investment opportunities in Seattle, Portland and Los Angeles, and later enter the San Diego and the Bay area markets.

Sanjay Bhatt: 206-464-3103 or On Twitter @sbhatt