Former Olympic swimmer Gary Hall Jr. says fleeing from the L.A. wildfires this week was a horrifying experience -- as he had only seconds to get out -- and it's clear he's disappointed he couldn't save his Games medals as he hastily evacuated.

The 50-year-old -- who earned 10 pieces of hardware in the 1996, 2000 and 2004 Olympics -- sat down with Harvey and Charles on Thursday's "TMZ Live" to detail how he escaped the flames that have been ravaging L.A. this week ... and he said it was everything but easy.

Hall Jr. says the blaze came on him and his house so quickly -- he only had "probably tops of three minutes" to get some belongings and get out.

The U.S. Olympic Hall of Famer said he grabbed his dog, some insulin, a painting of his grandfather and a religious work ... and he bolted.

Minutes later, he said he was on the phone with his girlfriend, who was just miles away, trying to help her find a route away from flames too.

"She was trapped," Hall Jr. said, "and she's seeing people jump out of their cars and start running for their lives."

Thankfully, both she and Hall Jr. made it to safety ... but he did say he was heartbroken his prized medals didn't make it out with him.

"I really wanted to hand those off to my kids," he said.

Nonetheless, Hall Jr.'s grateful to be OK ... and it's obvious his thoughts and prayers are with everyone who's still dealing with the impact of the blazes.