OAKLAND — Downtown Oakland is getting a new office tower that will incorporate the old Key System headquarters into a development that suggests the East Bay’s largest city is poised for an influx of companies and other organizations.

In addition to building a new tower, the project will renovate the historic former headquarters for the Key System — a privately owned mass-transit system of rail lines and buses that operated through much of the East Bay from 1903 to 1960, when it was sold to the newly formed AC Transit system.

The new tower and old Key System building will be connected.

“Part of what we want to do is bring this historic treasure back to life,” said Melinda Ellis Evers, a managing principal with San Francisco-based Ellis Partners, a developer that has teamed up with Intercontinental Real Estate in a joint venture to build the tower.

The project will take close to two years to build and should be available for tenants to move in by the end of 2019.

“We have over 50 percent of the building pre-leased,” said Ellis Evers.

The University of California Office of the President said in February 2017 that it has signed a lease at 1100 Broadway. Ellis Evers said the building’s first tenant leased 165,000 square feet of the 334,000-square-foot tower.

“This Ellis project demonstrates that Oakland’s time has come,” said Edward Del Beccaro, senior management director of the Oakland, Walnut Creek and San Jose offices of Transwestern, a commercial real estate brokerage. “Downtown Oakland has a strong office market.”

In addition to the Ellis-Intercontinental building, Shorenstein Properties is constructing a 400,000-square-foot office building at 601 City Center in Oakland.

And CIM Group, a veteran developer, has bought from Uber Technologies the old Sears building in downtown Oakland. It plans to complete a wide-ranging renovation of the property, now known as Uptown Station. The development is slated to be a mixed-use office and retail building.

With half of the 1100 Broadway building spoken for through the UC Office of the President rental deal, the Ellis firm is eyeing multiple possibilities for one or more tenants that would occupy the remainder of the tower.

“We want to create the most flexible, state-of-the-art office building in Oakland,” said James Ellis, managing principal with Ellis Partners. “We have open floor plans. We could get a single tenant for the upper floors of the building, we could have tenants that take multiple floors, or more than one tenant on a floor.”

Modern mass transit will be a crucial element in promoting the new building, which is next to a BART station.

“The last five or six years, the criteria tenants use to evaluate this location has completely changed,” Ellis said. “Tenants are really demanding that they are much closer to mass transportation than they used to.”

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“The sources of tenants will be those that are indigenous to the East Bay and are expanding, migration tenants from San Francisco, local technology companies that are expanding in Oakland or other parts of the 880 corridor, or government agencies,” Del Beccaro said.