SAN JOSE — Riverpark Towers, a striking downtown San Jose office complex of two highrises, is fully leased, marking a major success story in the urban core of the Bay Area’s largest city.

A burst of leases with tech firms and other companies has brought Riverpark Towers to a jaw-dropping milestone of 99.8 percent full, according to experts from Newmark Knight Frank, a commercial real estate firm handling the marketing of the building.

For the last two years, Newmark Knight Frank brokers Anne Ralston, Phil Mahoney, Michael Saign, and Joe Kelly have scouted for tenants to lease spaces in Riverpark Towers, whose owners are DivcoWest and Rockpoint Group.

“Riverpark Towers has incredible unobstructed views and we have the closest building to the Diridon train station,” said Ralston, a senior managing director with Newmark Knight Frank.

The leasing surge at Riverpark Towers also points to a major upswing for office properties in downtown San Jose.

It wasn’t that many years ago that experts viewed downtown San Jose as a moribund office market with high vacancy levels and sluggish rents that took a back seat to tech hubs with low vacancy levels such as Palo Alto, Mountain View, Cupertino, and Sunnyvale.

In the last year or two, office rents have jumped in downtown San Jose and vacancy levels have steadily dwindled to the point that office spaces have become tough to find.

“That’s the story of downtown San Jose,” said Scott Knies, executive director of the San Jose Downtown Association. “People have this perception that downtown is a certain way, and then it outperforms.”

The Newmark Knight Frank brokers have used deals with up-and-coming tech firms such as Sage Intacct and Cohesity, along with space-sharing pioneer WeWork, to steadily fill up the two towers. The realty agents also made efficient use of floors as they became available and shifted tenants.

As some tenants such as Acer exited Riverpark, the brokers grouped consecutive empty floors together to make the spaces more attractive to other companies.

Leases with two more tenants are now awaiting final signatures, and those deals would mean Riverpark Towers is about as full as it can get.

About two years ago, when the Newmark Knight Frank brokers took over the leasing, one of the two Riverpark highrises was just 62 percent full. The remarkable turnaround has brought the occupancy to 99 percent-plus.

Riverpark Towers contains about 600,000 square feet of office space. Tower 1 totals 297,000 square feet, while Tower 2 is 303,000 square feet, according to the DivcoWest website. DivcoWest and Rockpoint bought Riverpark Towers in December 2017, paying $283 million.

“In two years, we have signed leases for 519,970 square feet at Riverpark,” Ralston said.

The Newmark brokers also have accommodated a hiring boom by both Cohesity and Sage Intacct.

When the two tech upstarts signed their initial leases in Riverpark Towers, they each took roughly 40,000 square feet, Ralston recalled.

Now, Sage Intacct and Cohesity both occupy about 160,000 square feet, a stunning four-fold increase for both companies.

“Both companies have been able to hire more people and really expand in Riverpark,” Ralston said.

The steadily improving occupancy levels have also served to shove rents higher at Riverpark Towers. When DivcoWest and Rockpoint took ownership of the two towers, rents in the building were around $4.40 a square foot, according to Ralston.

“We thought that was a lofty rate at the time,” Ralston said. Since then, rents have risen to $5.30 a square foot in the complex. Ralston added, “Five years ago, our team never saw this coming, especially in downtown San Jose.”

Office vacancy rates were around 17 percent in San Jose during 2017, according to reports from major commercial property brokerages. Now, Ralston estimates that they are at 10 percent in downtown San Jose. “After this quarter it will drop below that,” Ralston said.

The intense interest in downtown San Jose by tech titans such as search colossus Google and cloud services giant Adobe has also spurred interest.

Near Diridon Station, Google has proposed a mixed-use transit village of office buildings, hotels, shops, restaurants, homes, entertainment hubs, and cultural centers, where tech titan would employ 25,000 people.

Adobe will dramatically expand its three-building downtown headquarters campus with a fourth office tower that’s now under construction.

Jay Paul Co., one of the Bay Area’s major developers, has broken ground on an 875,000-square-foot office tower at 200 Park Ave. that’s expected to be a dramatic addition to downtown San Jose’s skyline and take shape as a campus for a high-profile tech company.

“What’s going on at Riverpark Towers is a high-water mark for downtown San Jose,” Knies said. “That’s why you see Jay Paul under construction with the first speculative office project since Riverpark Tower 2.”