After attracting Philips North America as anchor tenant for its 250 North St. office building at Cambridge Crossing, developer DivcoWest is beginning construction of a 500,000-square-foot office-lab building to meet the strong demand for commercial space in East Cambridge.

DivcoWest hopes to duplicate its recent success and establish the 2.1-million-square-foot commercial component as a new tech and life science cluster.

DivcoWest has begun excavation and foundation work for the second building, Managing Director Mark Roopenian said. The site will be served by a relocated Lechmere station on the MBTA Green Line as part of its extension to Somerville and Medford.

Developers and officials gathered at the 45-acre site spanning the Boston, Cambridge and Somerville borders on Friday to mark the completion of steel framing for 250 North St., a 425,000-square-foot office building scheduled for completion in late 2019. Approximately 2,000 Philips employees will work at the new facility.

Philips sought to expand its Cambridge presence after opening its offices at 2 Canal Park in 2015, spurred by a five-year research partnership with Massachusetts Institute of Technology. The Cambridge Crossing headquarters will be a hub for Philips’ medical imaging research used for detection of cardiac and respiratory disorders and cancer, said Mark Mattern, chief financial officer for Philips North America. Philips will become one of the six largest private employers in Cambridge, he said.

“By moving to Cambridge Crossing, it not only puts us closer to our partners and customers, but it allows us to expand and work with leading startups,” Mattern said.

DivcoWest acquired the NorthPoint property in 2015 from Canyon-Johnson Urban Funds and HYM Investment Group for $291 million. Three residential towers totaling 2,500 units were completed under previous owners, and the total buildout calls for 4.5 million square feet of commercial and residential space.

A 15,000-square-foot retail building in the current phase of construction will house tenants including a brewpub and restaurant, and 250 North St. includes another 15,000 square feet of retail space.

John Moriarty & Assoc. is construction manager for the union-built project.

This article has been updated to correct the total square-footage of development.