Officials say the explosion was caused by a natural gas leak. Investigators were expected back on the scene Tuesday morning to determine exactly what caused the leak.
The homes located at 426, 428 and 430 Daly Street were leveled.
Officials say 428 Daly Street was a permitted construction site.
The Fire Marshal, the Department of Licenses & Inspections and the Philadelphia Gas Works are investigating the cause of the gas leak and PGW has shut off gas service to that block.
Action News has learned four construction permits have been pulled for 428 Daly, the house where the investigation is focusing.
L&I says work for three of the four permits was complete, and cleared by inspectors on Friday. The remaining permit was for electrical work.
One of those injured in the explosion was a contractor working on a water heater in the basement of 428 Daly Street.
He is listed in critical condition with burns over 22 percent of his body. He was being treated at Temple University Hospital's burn unit.
"There was a fella who was all burned up, the firemen were hosing him down with a hose," said witness Michael McGraw, who saw that contractor shortly after the blast. "He was really in bad shape."
Seven people are being treated at Thomas Jefferson University Hospital with minor injuries.
WITNESSES HEARD THE BLAST
The collapse happened around 11:00 a.m. Witnesses reported hearing the explosion.
"All of a sudden I hear this huge boom and look out my front window, and you can see debris flying and people screaming. So we knew it was time to get into action and get moving," said Jessica Rowe.
Several residents said they smelled gas prior to the blast.
"As soon as I felt the house shaking, I opened the windows and instantly smelled gas and stuff like that," said Tishon Jones. "That's when cops started banging on doors as hard as they could and telling everyone to evacuate out the house."
The injured include two babies from two different houses, a one-month-old and a three-month-old.
The woman who lives in 430 Daly Street, Sekeya Fields, said her 15-year-old daughter was inside her second-floor bedroom when the explosion occurred.
First responders found the teenager downstairs in the kitchen. Incredibly, she suffered only minor injuries.
Fields was on the phone with her boyfriend, who was outside in front of the house, when the blast happened.
"I was speaking to him on the phone when it all started. It sounded like it was car crashes happening simultaneously. All he said was 'Babe, the house is falling down," and before he could finish anything else the line went dead and I rushed home."
CELL PHONE VIDEO OF THE AFTERMATH
Action News obtained cell phone video that shows the aftermath of the South Philadelphia row home explosion moments after it happened.
No emergency vehicles, no firefighters, just rubble on the 400 block of Daly Street.
Erik LaSalle was in the area and recorded the video and firefighters arriving on the scene.
"I saw the house collapsing, I saw it going down. I saw the debris and smoke and dust flying out into the street," he said.
There was an enormous amount of damage to the homes and the vehicles on the street.
A Kia sedan was crushed by falling bricks and other debris. It belongs to Bonnie Sender. The Bear, Delaware woman was visiting her sister who lives on the next block.
Sender spent time looking for that parking space she finally found right in front of that home on Daly.
"I didn't think it was my car," she said. "I thought to myself, 'Oh my God, it can't be. Of all the cars, how could it be my car?'"
Sender was supposed to leave around 11am the time of the explosion.
Instead, she decided to stay with her sister a little longer and have that extra cup of coffee.
"My sister's been a wealth of strength for me and for each other. And now she is also the reason my life was saved," she said.
Sender recently lost her husband and mother so she's been through quite a lot lately.
That car was one of the last items she and her husband bought together. So while it has sentimental value, she says of course it can be replaced.
Witness Danielle James told Action News she felt her whole house shake.
"I thought it was on my block and I looked and saw it was behind us," she said.
James went on to say she and her family had smelled natural gas on Sunday night, but didn't know where it was coming from.
Christie Scibblo, a 26-year-old mother of four who lives four houses down from the collapsed home, said "I ran outside and I saw a firefighter rescuing an infant."
Firefighters worked through the afternoon to shore up the collapsed row houses, as residents wondered when they would be allowed to return to their own homes.
"We won't let them back until we know the scene is definitely safe," said Deputy Fire Commissioner Derrick Sawyer.
The 400 block of Daly Street was evacuated, along with the nearby portion of Wolf Street.
An evacuation center was set up at the Taggart Elementary School at 4th and Porter.
Monday afternoon the Red Cross was told that 70 homes were evacuated, and 26 people have been to the evacuation center.
By 11:00 p.m. Monday, Action News was told that most of the south side of the block remained evacuated because the electricity was still off, but the Office of Emergency Management believes the homes not directly damaged in the collapse are structurally okay.
Most residents on the north side of the block had been allowed back to their homes expect those directly across from the collapse site.
Monday's collapse came less than two months after a collapse at a Center City Philadelphia demolition site killed six people and injured 12 when a large wall fell on an adjacent thrift store.
A machinery operator has been charged with involuntary manslaughter in that case, and a grand jury is weighing whether anyone else should be charged.