"It was an egg-shape sewer, they don't make them like that anymore, they make them round and it was built by hand with masonry and bricks. Now they make them of clay," San Francisco Public Utilities Commission spokesperson Jean Walsh said.
According to the city's Pubic Utilities Commission, 30 percent of the city's sewer pipes are more than 100 years old.
PHOTOS: Crews rescue family from car after it got stuck in sinkhole in SF
It happened on Mission and New Montgomery streets. Crews rescued a family from the Uber vehicle that got stuck in the sinkhole. They were on their way to the airport when the incident occurred.
Buses have resumed travel through the area. The 14-Mission and 14R-Mission Rapid buses returned to their regular routes around 10 a.m. Wednesday after the curb lane reopened on Mission Street between New Montgomery and Second streets, according to Muni spokesman Paul Rose.
Repairs were slated to begin Wednesday morning on the roughly 12-by-5-foot sinkhole, which opened up at 5:30 p.m. Tuesday, according to the San Francisco Public Utilities Commission.
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The hole is roughly nine feet deep, and a broken sewer main was found at the bottom.
For now they will shore up the sides of the sinkhole and put a temporary blue bypass while they wait for the new sewer pipe to arrive from Arizona.
That work will be done on Friday and over the weekend without any service interruptions.
The cause of the sewer break is not yet known, but age is likely a factor, according to the SFPUC. That segment of the sewer line is made of brick and dates back to 1875.
One lane of traffic now opened on Mission St. & New Montgomery where sink hole occurred. pic.twitter.com/thFk4plIXG— Lyanne Melendez (@LyanneMelendez) May 11, 2016
A lane in each direction next to SF's sinkhole on Mission St. has been opened. pic.twitter.com/GPTTsYoTUX— Amy Hollyfield (@amyhollyfield) May 11, 2016
Giant sinkhole at New Montgomery and Mission in SF is giant pic.twitter.com/DiL4GH1e63— Sean Lynch (@sean_lynch) May 11, 2016
Bay City News contributed to this story.