Evacuations were lifted late Wednesday night in San Francisco's South of Market neighborhood after fire officials confirmed a heavy piece of equipment on the 30th floor of a skyscraper under construction was no longer in danger of collapsing.

Firefighters in the afternoon ordered evacuations from 16 buildings while they responded to and investigated reports of an unstable structure on top of the building at 41 Tehama St.

Neighboring sites at 543, 531, 527, 505, 547, 555, and 557 Howard Street, 44 Tehama Street and 235 Second St. were also asked to evacuate as a precaution.

All the evacuations were lifted except at 41 Tehama, officials said.

A crane and pump sitting on top of the structure in question caused concerns about its stability.

"We were able to determine the crane was not affected, but the pumping station was affected," fire spokesman Jonathan Baxter said.

Crews worked for three and a half hours Wednesday night to stabilize and level out the platform to be sure the 19,000-pound pump remains in place.

Fire officials at an earlier news conference said city engineers and building construction crews had secured the structure. In addition, fire officials said there was no imminent threat to the public.

"During the process of normal construction in a high-rise building, a platform was shored up and held in place with some struts — one of the struts in the northeast corner had failed, and when that failed, the platform itself leaned at a 15 degree angle," explained Assistant Fire Chief Tom Siragusa. Construction crew contacted SFFD, who ordered the evacuations based on the preliminary information. Siragusa said crews will be working to secure the unstable platform. Once the platform is stabilized, crews will be working to lower a heavy pump sitting on top of it.

"Our number one concern was the workers and public safety," he said. 'We erred on the side of caution."

Fire officials initially reported an unstable concrete slab on the 30th floor of the building, which they said weighed around 2,000 pounds.

But a statement from Hines and Invesco Real Estate, the developers for 41 Tehama, which is now being advertised as 33 Tehama, said the concrete slab was not in any danger of falling:

"This afternoon, an incident occurred at the 33 Tehama site between levels 35 and 36 where an interior forming system had a partial hydraulic failure while being raised to the next level. The interior forming system and the concrete placement arm have been secured and are being evaluated by engineers to bring it back to level.

No injuries and or damage has been reported.

Please note the boom is located in the center of the top level. This is not the crane attached to the outside of the building. Previous reports that a 2,000 pound slab of concrete is in danger of falling are also false."

Hines is also listed as one of the developers of the nearby Salesforce Tower, which is being built adjacent to the Transbay Transit Center in San Francisco, and is projected to become the second tallest building on the West Coast.

According to its website, 33 Tehama is a 37-story, 403-unit luxury residential tower, also near the Transbay Transit Center site. It began construction in 2015, according to a 2015 statement from the contractor Lend Lease. The project is designed by Arquitectonica and will feature a fitness center, clubroom, rooftop solarium, outdoor terrace, and ground-floor retail/art space.

A permit application for the construction project, which was filed in 2015, lists the cost of the project at $106,869,000.

In January 2016, a contractor called Pacific Structures Inc. filed a permit application for a tower crane to work on new construction at 41 Tehama. The estimated cost was $100,000. The contractor for the actual construction permit is Bovis Lend Lease, Inc.

Records from the Office of Safety and Health Administration, from the U.S. Department of Labor, reveal both Bovis Lend Lease and Pacific Structures have a history of violations.

San Francisco Fire Department Assistant Chief told reporters at a news conference that if the concrete slab fell down, there would be damage to nearby buildings. The California Highway Patrol closed down the Fremont Street offramp as a precaution. An engineering expert will be flying in from Washington to investigate the situation. Multiple agencies, including the San Francisco Municipal Transportation Agency, San Francisco Police and CHP assisted SFFD with the high-rise emergency.

Those working at nearby buildings that were evacuated tweeted out photos from the scene. Conor Murphy, who works at the shared office space, Galvanize, tweeted: "When @galvanize gets evacuated for an issue with a nearby building, class continues in the street!"

Scott Manley tweeted out photos of crowds and law enforcement officials gathering outside on the street as news of the evacuations broke around 3:30 p.m.

"Our office was just evacuated because the 33 Tehama crane might fall," tweeted David Spinks who works at the LinkedIn building on 222 2nd St.

Assistant Fire Chief Tom Siragusa says a construction company was in the process of placing a crane atop a building when a strut that helps hold the 30-ton crane up failed.

NBC Bay Area's Rachel Witte and Jean Elle contributed to this report.