Thousands of residents across three Massachusetts communities were told not to return to their homes Friday morning after a sudden series of gas explosions and fires ravaged the area in the Merrimack Valley the evening before. The explosion left one dead and more than 20 injured, one critically.

As many as 80 buildings were burned as terrified residents reported a blaze, an explosion, or the smell of gas. Fires lit up home after home as emergency responders attempted to extinguish them with hoses that were losing pressure from being overburdened. Firefighters were fighting multiple blazes at a time.

Hundreds of public safety workers from Eastern Massachusetts and Southern New Hampshire descended on the area Thursday evening. Andover police spokesman John Guilfoil said that in that town alone more than 200 firefighters were working at the peak of the crisis, along with 30 Andover police officers, 209 members of regional SWAT teams, and 13 State Police troopers.

According to authorities, some 8,600 homes or businesses in the towns of Lawrence, Andover and North Andover, north of Boston, were affected by an overpressurized gas line operated by Columbia Gas of Massachusetts. Stunned residents were told to immediately evacuate their homes, and most left with only the clothes on their backs, gathering up children and pets.

Dazed residents left the area, some by foot, others by car. Those who had no nearby relatives were told to go to five shelters that were hastily opened, and about 400 people ended up staying in these shelters overnight. Family members used cell phones and social media to try to locate loved ones who had been at school or work when the blasts began just before 5 p.m.

Electricity was also cut off to avoid igniting any gas. As night fell, local news helicopters recorded an eerie scene as the only light visible came from the headlights of vehicles jamming I-495 and emergency vehicles in the affected area that was cordoned off. As of Friday afternoon, some 18,000 National Grid electrical customers in the three communities were still without power.

“It looked like Armageddon, it really did,” Andover Fire Chief Michael Mansfield told reporters. “There were billows of smoke coming from Lawrence behind me. I could see pillars of smoke in front of me from the town of Andover.” News footage showed some houses reduced to rubble, reminiscent of a war zone.

Killed was 18-year-old Leonel Rondon of Lawrence. Rondon had just gotten his license and was sitting in a car parked in the driveway with three friends when the house exploded. His friend Christian Caraballo told the Boston Globe, “We heard a noise, then we felt it again and heard it. I seen the front of the house explode to the street.” The walls of the house collapsed, then the chimney fell on the car, severely injuring Rondon, who died later at the hospital. His friends suffered lesser injuries.

Lawrence, where Rondon lived, is a larger and far poorer city than the adjoining towns of Andover and North Andover. Lawrence was once a thriving mill town, attracting immigrants from around the world to work in its mills. With the decline of manufacturing in the 1950s, the city suffered a devastating economic decline. In 2016, the median household income was about $26,000, compared to the US average of $42,000.

Columbia Gas technicians accompanied by firefighters, police or local officials began visiting every one of the 8,600 homes and businesses in Lawrence, Andover and North Andover affected by Friday night’s events to shut off each gas meter and conduct a safety inspection. Residents can return to their homes only when their blocks are listed as safe on their city or town’s web sites.

Authorities say it will take days, not hours, for their inspections to be completed. Once residents are allowed to return to their homes, they are required to call the gas company to have their gas meters turned back on. While electricity may be restored within days to some homes, it may be weeks before gas service restored.

Residents have received little to no information from Columbia Gas about why the explosions happened or when they can expect to return to their homes. The gas company dispatched representatives to answer questions, but repeatedly told angry residents that they had “no answers.”

One woman asked whether it was safe to run a generator, and the Columbia rep said she didn’t know. Milton Valencia of the Globe tweeted Friday: “I am in No. Andover and Columbia gas reps just ran away from residents who were bombarding them with questions they didn’t know the answers to.” The rep told the residents that he “would take your questions back” to the company.

Columbia Gas is part of NiSource, a utility company with 3.5 million natural gas customers and 500,000 electric customers in seven states: Indiana, Kentucky, Maryland, Massachusetts, Ohio, Pennsylvania and Virginia. The company has not given any explanation for Thursday’s incident, saying only that they were investigating its cause.

While Columbia Gas has been tight-lipped, Kurt Schwartz, the state’s head emergency management official, said at a Friday morning news conference that more than 8,000 gas meters were fed by “distribution lines that were overpressurized.” He said that the investigation would focus “on the distribution system and the origin of the pressure.” Experts indicate that overpressurization could be caused by someone opening a valve or a mechanical failure on a control valve.

A press release posted Thursday on Columbia Gas’s website, before the explosions, announced work to upgrade natural gas lines and improve service, three ongoing projects in Lawrence, four in Andover, and two in North Andover. It is unclear whether these projects had any connection to Thursday night’s events.

In the months leading up to the incident, Columbia Gas sought to raise rates for consumers by $44.5 million, which they claimed was necessary in part to cover operating costs to comply with federal and state safety regulations that were causing a “revenue deficiency.” Columbia Gas agreed just last week to reduce the distribution rate increase for its 321,000 Massachusetts customers by about $11 million, to $33.2 million.

A subsidiary of NiSource, Columbia’s parent company, was blamed by federal investigators for its role in a previous pipeline rupture in Sissonville, West Virginia The explosion and subsequent fire destroyed three homes, melted the siding on nearby houses nearby, and heavily damaged an interstate highway, according to federal reports.

Whichever for-profit company sells gas in the Merrimack Valley or oversees the response to the explosions, the area is served by some of the country’s oldest and most leak-prone pipes. Columbia Gas has more miles of old, cast-iron gas mains than all but 15 utilities in the US, according to a USA Today analysis of federal safety data.

The analysis shows that about every other day over the past decade, a gas leak in the US has destroyed property, hurt someone or killed someone. Since 2004, the most destructive explosions have killed at least 135 people.

Because the energy conglomerates are not willing to pay the estimated $1 million per mile to replace these aging pipes—unless customers pay to offset any drain on their profits—communities such as those in the Merrimack Valley are sitting on virtual time bombs in the form of potentially deadly leaking gas pipes.