The tallest office tower to be built in Denver since the 1980s is beginning to leave its mark on the city skyline.

Nineteen months after breaking ground, Hines’ 40-story skyscraper, 1144 Fifteenth, is rapidly taking shape at the corner of 15th and Arapahoe streets. As of midweek, the building’s core was at 32 stories and counting and the steel decks were not far behind.

At street level, the progress may be even more eye-catching — all but one of the building’s 11 above-ground parking levels are encased in the reflective glass that will cover the 603-foot-tall tower. On a sunny day, you can catch of a glimpse of the historic Daniels & Fisher Tower as you walk by.

“We can’t wait for people to start noticing this building,” Hines senior managing director Jay Despard said. “Unless you’re in real estate, you don’t necessarily pay attention to what’s going on on the skyline until it’s, like, ‘Where did that come from?’ We’re about to be at that point where people driving around are going to be asking, ‘What is that?'”

The $300 million skyscraper should reach its final height — “topping out” in construction speak — in late June or early July, with the project on schedule for an early 2018 opening.

When complete,1144 Fifteenth will be the fifth-tallest building in Denver — the fourth tallest if you ignore the 75-foot spire atop the Four Seasons Hotel and Residences next door.

Leasing is ahead of schedule, Despard said, with 30 percent of the spec building’s 670,000 square feet under contract.

So far, two tenants have been announced. Gates Corp., a leading manufacturer of power transmission belts and fluid power products, will take 125,968 square feet, and cybersecurity firm Optiv has signed a lease for 75,692 square feet, according to JLL, which is handling leasing for the project.

Both companies plan to consolidate their downtown office presence in the new building, according to a JLL spokeswoman.

Despard said full lease-up should be completed within a year and a half to two years after the skyscraper opens. Law, financial services and private equity firms have been among the prospective tenants. (The building’s office space starts on the 14th floor.)

“When we started this, we thought there would be more interest from oil and gas, but since that went away, it’s not turning out that way,” he said. “From a building standpoint, it’s better to have a diverse mix of groups. We’re off to a good start.”

While some real estate experts have projected a moderate slowdown in the office market nationwide this year, Despard said being Denver’s only new office skyscraper in three decades should benefit 1144 Fifteenth.

“This building is such an anomaly it has its own little demand pocket,” he said. “Are there tenants that are looking for this product? If they are, this is it.”