HAYWARD -- Five people escaped with their lives, including a 3-year-old boy thrown from a second-floor window to waiting hands below, after a fire ripped through an apartment Thursday night, authorities said.

The blaze, which broke out about 11 p.m. at a two-story, four-unit building on the 22000 block of Seventh Street, was one of two in the area within hours of each other; fire crews also extinguished a fire in a carport located behind an apartment on the same block Friday morning, fire spokesman Don Nichelson said. Nobody was injured in the second one, but it destroyed more than a half dozen cars.

Fire crews were calling the carport blaze suspicious, and investigators told reporters that it was being treated as a crime scene.

"Cars don't just self-ignite," Batallion Chief Nathaniel Armstrong said at the scene.

Investigators said the fire at the apartment began on the stove and that five people -- the boy, his grandparents, his great aunt and his uncle -- were home when it started.

"The boy's uncle said he had some oil on the stove and was getting ready to cook something," Nichelson said. "He walked away and when he came back he tried to put it out but it was too late."

Investigators were trying to piece together how a small kitchen fire was able to spread so quickly, barring the residents from leaving. The boy was trapped upstairs in the two-story unit with his grandparents, Nichelson said.

Neighbors said the boy's grandparents fell asleep and were unable to get down the stairs when they awoke because of the heavy flames and smoke.

"People came knocking on our door and shouted, 'There's a fire, there's a fire! Get out, get out!'" said neighbor Danny Cummings, 22. "We could see the flames shooting out."

Yolanda Lindsey, who lives in the unit directly below, said that before she knew the apartment was on fire she dialed 911 to report what she thought was a home-invasion robbery taking place upstairs.

"I called 911 and I'm like, 'Come quick they're killing them,' but it was them running trying to see how to get out of there," Lindsey said.

The boy's uncle and great aunt were downstairs and able to escape through the front door, Nichelson said. The aunt eventually went below the second-floor window that Nichelson said was about 25 feet above the ground.

At that point, the boy's grandparents dropped him out of the window into the waiting arms of his aunt, Nichelson said. Then they jumped out the window themselves.

All three were taken by ambulance to a Eden Medical Center.

The grandmother suffered serious injuries with cuts to her head and damage to her hips and pelvis, Armstrong said. The grandfather broke his ankle. The boy was unhurt

No other injuries were reported and crews put out the fire in about 15 minutes.

In all, 12 people in the building were displaced -- five of them were residents who lived in the unit that caught fire, Nichelson said.

The fire department called the American Red Cross to assist in relocating the residents.

In all, the fire cause about $200,000 in damage to the building which Nichelson said was valued at $450,000. The other three units sustained smoke and water damage.

About six hours later, the carport fire began, Nichelson said. The carport also is located in the 22000 block of Seventh Street, about 60 or 70 yards from the apartment that burned. Only one structure is between the two, he said.

The timing and the instantaneous nature of the carport fire are suspicious factors, Armstrong said. Investigators were at the scene Friday morning, searching for an incendiary device. No injuries were reported in the carport fire.

Contact Rick Hurd at 925-945-4789 and follow him at Twitter.com/3rdERH. Contact Karina Ioffee at 925-847-2112 and follow her at Twitter.com/kioffee