SOUTH LOS ANGELES (CBSLA.com) — The LADWP is still trying to figure out the cause of an underground explosion Wednesday on a busy street in South L.A.

Several streets remained blocked off through Wednesday night at Brynhurst Avenue and 63rd street in the Hyde Park neighborhood.

The blast happened around 3:30 p.m. Wednesday, sending asphalt and two 250-pound manhole covers flying.

Brian Jefferson and his brother Adrian live right next to where it happened.

“I just heard a real loud sound, kind of like a boom, like there was truck accident,” Brian Jefferson said.

Incredibly, no one was hurt in the blast, but several parked cars were damaged and windshields were shattered.

“I heard this big old explosion like consecutively four times in a row, and I was like ‘Whoa, what was that?'” Adrian Jefferson said.

Investigators say it appears an underground electrical vault exploded.

“Electrical vaults from time to time will overheat and explode just because they get so hot,” LAFD battalion chief Kris Larson said. “There’s energy running through them and there’s heat behind it. It’s just unusual that it happened on a day that’s not extremely hot.”

And with so many children who live and play nearby, folks who live in the area know the blast could have been a lot worse.

“I’m glad that nobody was hurt and everybody’s OK,” Adrian Jefferson said. “I mean, it’s kind of like, I find it hard to believe … so many cars that go through.”