Construction is under way on the third tower in Amazon’s Seattle high-rise campus. When this phase is completed in 2019, the full block at Westlake and Lenora avenues will have a 37-story tower and a seven-story building with a total of 1.1 million square feet of office, more than 43,000 square feet of retail and 1,128 underground parking stalls. The block is where Toyota operated a dealership until moving to the Sodo neighborhood. Amazon already has two other new towers next door.

On Monday, Amazon employees began moving into Day One, the 36-story tower on the block west of the third tower site. The Day One block is where Amazon’s biosphere building, the centerpiece of the high-rise campus, is going up. It’s scheduled to open in the spring of 2018. The campus’ first tower, Doppler, opened in December. Together, the three blocks will have around 3.3 million square feet of office space, and Amazon is working on plans for a fourth block at 2200 Seventh Ave. This fourth block will have a 24-story tower and an eight-story building with another approximately 850,000 square feet of office, according to information on file with the city.

Amazon (Nasdaq: AMZN) does not disclose how many employees will work in this part of Seattle. But based on 175 square feet per employee, the four-block campus could accommodate around 23,700 employees. This is in addition to the company’s expansive South Lake Union campus. On its website, Amazon says it now employs more than 20,000 people in Seattle, and is the city’s largest private employer. Amazon confirmed last year that it would start building the third tower this fall, and now it is. Last month, the company moved its Prime Now fulfillment center on the site of Tower III to Sodo. Seattle architecture firm NBBJ designed the first three blocks, and general contractor Sellen built the first two and is working on the third one as well.