From the outside, the bubble-gum pink warehouse on Shafter Avenue in San Francisco’s Bayview district looked deserted since the city issued a restrictive shelter-in-place order to curtail the spread of the coronavirus.

The March 16 order forced all non-essential businesses to immediately close, including the janitorial company that used the warehouse tucked away at the end of a dead-end street to store extra materials.

But San Francisco authorities said Monday that the building at 2266 Shafter Avenue was far from closed—and instead, it was being used as an illegal underground nightclub that attracted more than 150 partygoers over a 48-hour period.

In a time-lapse video released by the San Francisco City Attorney’s office, more than 20 to 30 cars can be seen parked outside or leaving the building over the weekend of April 4, with none of the club patrons practicing “six feet of social distancing.” The unlicensed after-hours club, which was operating between 2 a.m. and 6 a.m., even had a security guard who frisked visitors as they entered, prosecutors said.

“This pandemic is deadly serious. People need to treat it that way,” San Francisco City Attorney Dennis Herrera said in a press release, announcing that the club was shut down on Saturday for violating the public-health order. The civil inspection and abatement warrant authorities secured on Friday is the first used by the city to enforce the shelter-in-place order amidst the outbreak.

“We are going to use every tool at our disposal, including these types of warrants, to protect public health during this pandemic,” Herrera added. “Cramming dozens of people into an illegal club during this outbreak is like dropping a lit match in the woods during fire season. Who knows how far the damage will spread? It’s the epitome of irresponsibility.”

According to the San Francisco Chronicle, the warehouse was leased by Bay Area Pinnacle Cleaning in early February to park the janitorial company’s trucks and cleaning supplies. Within days of securing the property, however, the company allegedly turned over the warehouse to the owners of the after-hours club. The owners have not been publicly named.

Herrera told reporters on Monday that the landlords cooperated with the investigation, which began Friday after investigators received a tip about the illicit revelry.

During a stake-out on April 8, investigators saw multiple people coming and going from the club and “loud music could be heard emanating from inside.”

After obtaining a warrant on Friday, San Francisco police parked cars outside the warehouse in an effort to deter residents from entering the illegal club. But that didn’t stop partygoers from showing up in cars and taxis, checking in with a doorman at the warehouse’s front door, and hanging out at the club for hours.

On Saturday, officers from the San Francisco Tactical Unit and Bayview Station raided the warehouse, seizing “DJ equipment, two fog machines, nine gambling machines with $670 in cash inside, two pool tables, bins of liquor, cases of beer, bar furniture, and other nightclub-related items,” the city’s attorney’s office said.

“The operators of this illegal club senselessly put lives at risk in a time when our city is doing everything within our means to slow the spread of this pandemic and safeguard the health and wellbeing of the public,” San Francisco Police Chief William Scott said in a statement. “Let this case be a reminder that we will take action against those who knowingly violate the public health order and endanger the health and safety of our residents.”

The San Francisco Police told The Daily Beast no one has been arrested in connection with the nightclub, but declined to discuss details because of the “active investigation.” So far, no one has been issued citations or fines for violating the public-health order.

The San Francisco City Attorney’s office did not immediately respond to The Daily Beast’s request for comment.