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San Bruno, California (CNN) -- Firefighters have fully contained a massive gas-fueled blaze in California that killed four people, while search efforts and attempts to determine the cause of the fire were still under way on Friday.

The fire triggered by a ruptured natural gas transmission line sent giant fireballs shooting 80 feet into the air in a quiet neighborhood of San Bruno, near the San Francisco airport.

"It looks like a moonscape in some areas," said San Bruno Fire Chief Dennis Haag, who was visibly shaken at a news conference.

Scorched homes and the shells of burned-out cars lined charred streets as firefighters battled hot spots and residents clamored to know the cause of their town's devastation. By Friday afternoon, the fire was reported to be fully contained.

iReport: Lone fireman fights flames

California Lt. Gov. Abel Maldonado said he was shocked by the "horrible tragedy."

"It looks like a bomb went off," he said. "I saw debris everywhere. It was a huge explosion."

"Our hearts go out to those impacted by this horrible disaster," said Maldonado. "Without warning many of these peoples' lives have been changed forever and my deepest prayers go out to everyone."

He said "we will find out soon" what caused the fire that erupted after 6 p.m. Thursday after a gas transmission line broke and triggered an explosion. Maldonado also told reporters on Friday he had received a telephone call from President Barack Obama, who offered his support.

iReport: Another view of the fire

Four people are known to have died in the fire, the lieutenant governor said. Another 52 people were injured, including three patients who were taken to a hospital with third-degree burns and four firefighters who suffered from smoke inhalation.

Rescue workers initially feared the death toll would climb higher as they combed through the smoldering scene with cadaver dogs.

But by Friday evening, no one in the area was unaccounted for and local fire officials had not received reports of any missing people, according to Haag. He said about 100 people had evacuated to shelters.

Blasts, fireballs and quake-like rumbles

Search efforts were roughly 95 percent complete. The remaining 5 percent was still too hot to enter, the fire chief added.

Pacific Gas and Electric Company President Chris Johns said Friday that the ruptured gas transmission line had been secured and no more gas is flowing through it.

He said survey teams are walking house to house to "make sure it is safe" for residents to return, and he promised that the company will be transparent in working with federal investigators to learn the cause of the blast.

The National Transportation and Safety Board launched an investigation Friday.

Safety questions raised

"At this point, it's too early to speculate as to what may have happened," NTSB Vice Chairman Christopher Hart told reporters. He said a team of investigators was working on scene to determine probable cause. The group's findings will be put into a report that may not be ready for as many as 18 months, Hart said.

PG&E's Johns said he had heard accounts of residents complaining of the smell of gas for the past three weeks and the company was looking into whether any phone calls had come in.

"We are really saddened and sorry about this tragedy and we are going to do everything we can to help the folks who have been affected by this," he said.

The fire destroyed 37 homes and damaged eight, California Emergency Management Agency Secretary Matthew Bettenhausen told reporters. Those numbers were considerably lower than the estimate of roughly 170 homes that NTSB's Hart said were affected by the blaze.

The fire was about 50 percent contained four hours after it began, Haag said. But the intense, persistent flames made it difficult for crews to get close.

Gas pipes near homes, windy weather and water supply problems also complicated efforts to combat the flames.

iReport: Ground level view of fire

"The radiant heat from the actual gas and the fireball was making it so that they couldn't even attack the homes that were on fire," said news photographer Bryan Carmody, who arrived at the scene shortly after the blaze began.

Water pressure in the area was low because the fire compromised a water main, California state Sen. Leland Yee told CNN affiliate KRON, so firefighters had to truck in water.

James Ruane, the mayor of San Bruno, said he talked to survivors of the blaze to assure them that the city will help them. He said he could tell how much the incident affected them.

"It was the look on their faces. They were still in shock," he said. "They were walking around but almost in a daze. It must have been horrific when it happened."

Tim Gutierrez, who lives in a neighborhood near where the blast occurred, told CNN affiliate KRON that people living in the area have smelled natural gas for the past three weeks.

iReport: Video and photos of the fire

"Every day after work, I would smell the heavy smell coming from the gutter and sewer," he said.

Asked about that account Thursday night, Haag told reporters it was "the first time the fire department's ever had any notice of it."

Maldonado declared a state of emergency in San Mateo County.

The fire erupted in a populated area about two miles west of San Francisco International Airport.

All flights and operations there were normal Friday, according to the Federal Aviation Administration.

CNN's Dan Simon, Catherine E. Shoichet, Ninette Sosa, Shawn Nottingham, Anderson Cooper, Karan Olson, Sonya Hamasaki, Deanna Proeller, Greg Morrison, Scott Thompson, Amanda Watts and Moni Basu contributed to this report.