SAN FRANCISCO (AP) — San Francisco’s “Grand Central of the West” is closed out of safety concerns after workers discovered a crack in a support beam of the $2 billion transit terminal that opened just last month.

Workers discovered the crack early Tuesday while installing roofing tiles at the Salesforce Transit Center, executive director Mark Zabaneh said. Engineers spent the day inspecting the damage, and Zabaneh said they decided to shut down the station around 5 p.m., just as the afternoon rush hour started.

Zabaneh said the cause and the extent of the damage were unknown and the decision to close the terminal was made out of an “abundance of caution.”

“The behavior of the beam is unpredictable,” Zabaneh said.

He said structural engineers would continue inspecting the building Wednesday to assess whether it is safe for people to return.

The facility, a commanding presence in the city’s South of Market neighborhood where construction is booming, sits adjacent to the so-called sinking condominium, Millennium Tower, which has settled about 18 inches (45 centimeters) since it opened over a former landfill in 2009.

Homeowners have filed multiple lawsuits against the developer and the city, some alleging that construction of the transit center caused the Millennium Tower to sink.

Zabaneh said he did not believe the cracked beam was related to ongoing problems at Millennium Tower.

The crack was found near a weld on a stress-bearing horizontal beam, Zabaneh said. Engineers are searching for other cracks in other pipes but are optimistic the damage is limited to the one pipe.

Buses were rerouted to a temporary transit center about two blocks away that was used during the center’s construction. A downtown street that runs under the beam also was ordered closed indefinitely, causing traffic chaos at the same time some streets were closed for a conference sponsored by Salesforce that was expected to draw 170,000 attendees.

Enveloped in wavy white sheets of metal veil, the five-level center includes a bus deck, a towering sky-lit central entrance hall and a rooftop park with an outdoor amphitheater. Zabaneh said American steel was used in the center’s construction.

“A structural steel beam should never crack,” Joe Maffei of Maffei Structural Engineering told the San Francisco Chronicle.

The newspaper previously reported that the complex faced delays in putting out contracts to bid, and the winning bids were ultimately higher than expected.

The terminal’s cost rose from $1.6 billion at its 2010 groundbreaking to more than $2 billion in 2016 because of what one analyst called “optimistic assumptions,” according to the Chronicle.

The project is financed by land sales, federal stimulus grants, district fees and taxes, bridge tolls, and federal and state funds.

Numerous towering condo buildings have gone up in the booming South of Market neighborhood in the last five years and several multistory construction projects are still underway as San Francisco lures technology companies from Silicon Valley to the neighborhood.

The online business software company Salesforce, which opened its adjacent 61-story Salesforce Tower earlier this year, bought naming rights to the transit center in 2017 as part of a 25-year, $110 million sponsorship agreement.

The Salesforce Transit Center is operated by the Transbay Joint Powers Authority.