The San Diego Zoo is expected to reopen Friday after a gas leak one day prior forced the evacuation of the landmark.

Repairs to a broken 0.75-inch gas main supply were completed overnight. The gas line was ruptured Thursday morning by construction crews working on an ongoing renovation of the Children's Zoo area of the park.

San Diego Fire-Rescue Department crews and San Diego Gas & Electric officials were called to 2920 Zoo Drive at 8:11 a.m. Thursday.

An NBC 7 news photographer arrived soon after and captured video of the supply line leaking. The hissing sounds of air could be heard more than 30 feet away.

“Which you can hear, it’s under an extreme amount of pressure,” said SDFD Battalion Chief Rob Hartman while standing in front of the entrance to the zoo.

An SDG&E spokesperson said the utility's initial investigation shows the construction crew followed protocol by having SDG&E come to the work site and mark the underground lines.

The San Diego Zoo and several Balboa Park museums were closed due to a gas main break at the zoo. NBC 7's Liberty Zabala reports.

Everything that happened after that is still under investigation, the spokesperson said.

The zoo is open from 9 a.m. to 9 p.m., with extended evening hours that are part of its summertime "Nighttime Zoo," which runs through Labor Day. The main entrance was closed following the gas leak, and guests were initially rerouted to another side of the property.

Gas main break at the SD Zoo near the main entrance. SDFD has two crews and a battalion chief on scene and they are working with Zoo staff. Evacuations of the area taking place currently. Please avoid the area if possible. pic.twitter.com/v6Kpvgtvcs — SDFD (@SDFD) August 22, 2019

However, after 9:30 a.m., zoo administrators sent a message to employees calling for a zoo-wide evacuation.

At 10 a.m., a media representative confirmed to NBC 7 that the zoo would be closed to visitors for the day.

Golf carts were used to move zoo employees outside of the park after San Diego Zoo officials decided to close the park due to a break in the gas supply line near the main entrance. https://t.co/wpl2quuVzH pic.twitter.com/dcYkD4dYAS — NBC 7 San Diego (@nbcsandiego) August 22, 2019

Kim Wile was on a Lyft on her way to visit the zoo and she heard the evacuation information on the radio.

“I had hoped the leak would be fixed by now but obviously it’s not,” Wile said. “My day is a little side-tracked right now but it will be okay.”

San Diego Battalion Chief Rob Hartman talks with NBC 7 about the four-inch supply line that was spewing gas near the main entrance of the San Diego Zoo.

The animals were still in their respective enclosures.

"All animals at the Zoo are safe and secure," zoo officials said in a written statement.

“Where it’s at, it’s not affecting the animal enclosures,” Hartman said of the gas leak.

At 11:30 a.m., the leak was stopped. At that point, there was no time estimate for when the repairs would be completed.

“This is a supply line. Even if you shut down the valves it takes a while for the pressure to bleed off so they can come in and do the repair work," Hartman said.

The gas leak temporarily closed Park Boulevard, a major thoroughfare in the busy area that connects the San Diego Zoo and Balboa Park and its many museums. By 11 a.m., all lanes were reopened; San Diego police were in the area directing traffic. Meanwhile, Zoo Drive between Village Place and Zoo Place remained closed to motorists.

The gas leak also forced the closure of several museums in Balboa Park including The Natural History Museum, San Diego Museum of Man, the San Diego Museum of Art and Fleet Science Center.

The Prado and Panama 66 restaurants at the heart of the park were also closed for the rest of the day.

Balboa Park museums that were not affected included the Japanese Friendship Garden, San Diego Air and Space Museum, San Diego Automotive Museum, and the Veterans Museum.

Several museums in Balboa Park closed due to a gas leak at the San Diego Zoo. NBC 7's Rory Devine has more.

Performances at the Old Globe and Spreckles Organ Pavillion were also not affected, Balboa Park said. The roads and pedestrian walkways at Balboa Park remained open Thursday.

Balboa Park said it expected to reopen all museums by Friday.

At 2:45 p.m., SDG&E confirmed details about the gas line that had ruptured, saying it was a 0.75-inch line. Originally, crews said the ruptured piping was a 4-inch line.

Currently, the zoo is undergoing a redesign of the Children's Zoo area of the park which is located near the front entrance in the southern area of the park. The area has been closed to guests amid the construction project.

San Diego Zoo Global released the following statement:

"At approximately 8:15 a.m. today (Thursday, Aug. 22, 2019), a gas line leak was discovered on Zoo Place, near the San Diego Zoo’s entrance. Out of an abundance of caution, Zoo security and local emergency services made the decision to evacuate San Diego Zoo staff and guests from the area, and closed the Zoo for the remainder of the day. All animals at the Zoo are safe and secure. San Diego Fire, San Diego Police, and San Diego Gas & Electric are on site, and we will follow their guidance."

No other information was available.