An early-morning water main break Wednesday flooded part of Chinatown and caused a pair of manhole fires that forced the evacuation of more than 100 people, closed about a dozen businesses for the day, and created traffic gridlock for hours.
The underground fires began sending toxic smoke into the street and surrounding buildings around 9 a.m., about four hours after a 20-inch cast-iron pipe gave way on Washington Street, city officials said.
The gushing water seeped into the manhole system on Kneeland Street and short-circuited it, causing fires that spewed high levels of carbon monoxide into the air, Boston Fire Commissioner Joseph Finn said.
Fire officials evacuated three to four buildings over concerns about the levels, which measured at 700 to 800 parts per million in some spots, he said.
Firefighters used a special foam to extinguish flames in the manholes, he said.
“The smoke and the fire and the heat can migrate into the buildings,” Finn said. “The [carbon monoxide] levels from the burning cables are very significant.”
Mayor Martin J. Walsh blamed the failure on the city’s aging infrastructure. The affected water main was installed in 1891 and was lined with cement to improve water flow in 1984, according to the Boston Water and Sewer Commission.
“It’s something that we have to look at,” Walsh said. “How do we replace these old pipes that we have in the city of Boston?”
Crews repaired the pipe by Wednesday afternoon, but cleanup and repaving work remained, said Stephen Mulloney, a commission spokesman. Officials haven’t determined why the water main failed, he said. Officials are tallying the amount of damage.
Roads in the area were closed for much of the day. Some businesses had to discard supplies, packages, and products that were soaked by the flooding, said Inspectional Services Department Commissioner William Christopher. The businesses must pass a health inspection before they can reopen, an ISD spokeswoman said.
Qian Wang, president of Jia Ho Supermarket, said about one-third of the dried goods kept in the store’s basement had to be thrown out. The damage will exceed $100,000, he estimated.
Wang also owns the Joy Luck Hot Pot Restaurant on Kneeland Street, which was also forced to close. By Wednesday afternoon, Wang said he hadn’t been able to make it there to assess the damage.
“I can do nothing,” he said. “Right now, I have no idea when we can open.”
The nonprofit group Chinatown Main Street is helping businesses file insurance claims and access city services, said executive director Courtney Ho.
“We’re not going to leave until we make sure they get the answers they need to get back into business,” Christopher said.
The restaurant Spicy World was among the businesses on Beach Street that reopened Wednesday afternoon. Owner Fan Huang said he lost about 20 customers because he was closed all morning, but that his business escaped without damage.
“I [saw] some regular customers stop by and feel disappointed because we were closed,” he said.
At HI Boston Hostel on Stuart Street, which was housing about 150 guests, some smoke seeped into the building and the emergency water pumps were activated because the water pressure dropped, said Marc Johnson, the general manager.
“It’s been a big disruption,” Johnson said. “There’s nothing we can do. You want to be safe.”
Some hostel guests said they left all their belongings behind when they were evacuated.
“All my stuff,” said Daniella Gough, 29, who is visiting from Cambridge, England. “My passport, my bag, everything apart from my phone. I’ve got my phone.”
Gough, a bakery manager, said she was one of the last people to exit the hostel.
“There are more fire engines than I’ve ever seen,” she said. “We don’t have this many in England.”
Hostel guests were allowed back in the building around noon after carbon monoxide levels dropped.
Eversource Energy, the utility that provides electricity to the neighborhood, said it was still assessing the damage to the two manholes that caught fire and the underground power cable.
Crews cut electricity to the affected manholes, and one building lost power for 45 minutes, said Michael Durand, an Eversource spokesman. Repair work will likely last a few days, he estimated.
Aimee Ortiz of the Globe staff contributed to this report. Laura Crimaldi can be reached at firstname.lastname@example.org.