A six-alarm fire -- the second on this street in three months -- ripped through a Redwood City apartment Thursday morning, forcing some residents to use rock climbing gear to escape to safety.

No major injuries and no deaths were reported at the 75-unit Terrace Apartments during the massive blaze first reported on the fourth floor about 5:30 a.m. in the 900 block of Woodside Road, or Highway 84. There were four injuries, though - two moderate and two minor, according to fire officials.

A total of 75 people were displaced.

RAW VIDEO: 6-Alarm Fire at Redwood City Apartment

Furious flames shot through the four-story building, and at one point, Redwood City firefighters worried the blaze would turn out to be a "multi-casualty" incident. It took crews about four hours to get the flames under control.

None of the units are inhabitable. Right now, no one is being allowed back in their old apartment.

Hours after the blaze was extinguished, as a precaution, police used cadaver dogs to search the rubble for any more victims.

Redwood City Fire Marshal Jim Palisi said people were lucky to get out, as the older building was not equipped with sprinklers. As of 2008, all newly built apartment buildings require sprinklers. Many older buildings are grandfathered in so that they don't have to -- by state code -- install them.

The cause of the fire is under investigation.

PHOTOS: Fire Rips Through Redwood City Apartments

Escaping injury were roommates Matt Fisher and Adam Carpenter. Both are rock climbers. They tied up cloth to semi-rappel down the building.

"I threw some wet towels on the door and from there, it was just quick grab for stuff," Carpenter said.

Residents who made it out alive were thankful -- and even feeling a bit spiritual.

"I'm just grateful that I'm alive," Valerie Russell told NBC Bay Area from the Red Cross command post set up at the Red Morton Community Center, where nearly 75 people, including a baby, had checked in.

"It's a blessing," added Devon Walker, who was rescued from unit 321.

Rob Sing was at the shelter in a blue cardigan, gray slacks and no shoes. He didn't have time to grab them before shimmying down a fire escape off the balcony. He lost all his belongings in the fire. But. still, he kept the loss of material things in perspective.

"I already cried it out," Sing said. "I feel much better now."

Linda Essex was another of the lucky residents to escape without a scratch.

"I heard a bell going off," she said. "I knew something was up. I peeked in the hallway, got my purse and ran out."

On July 7, another six-alarm blaze ripped through a 72-unit Redwood City apartment complex in the 500 block of Woodside Road, killing one and injuring nearly two dozen at the Hallmark House Apartments.

Attorney Ara Jabagchourian of the Burlingame law firm Cotchett, Pitre & McCarthy filed suit (PDF) against the owner of the apartment building, KDF Hallmark , which was not equipped with sprinklers. The building was built in 1964 and not legally required to have the sprinklers, but the lawsuit alleges the company was "negligent" in not properly "inspecting, maintaining and safeguarding the property from a foreseeable unit fire," the suit claims.

A call to KDF Hallmark was not immediately returned.

NBC Bay Area's Adrian Holeyman and Shelby Hansen contributed to this report.