Mr Harwood and another motorist worked quickly to get the boy and his family out of the car.
He cut the driver from his seatbelt using a knife tossed to him by a bystander and then went to rescue the three in the back. An elderly man was hunched over another child, and a woman was trapped.
"The fire reignited - that's when it started to get really nerve-racking," Mr Harwood said.
"The flames were starting to travel up and above us, it was pouring through the dashboard into the car. It was getting really close.
"I reached in and grabbed the last person, the mum, and yanked her out and just ran. Then the car exploded. We were just in time."
When Mr Harwood spoke to the Herald, he downplayed his bravery.
"It's a situation that had to be dealt with. We've got to do what we've got to do," he said.
It was not the first time Mr Harwood had featured in the Herald for heroism.
Last year, he rescued a woman trapped in her car during heavy flooding near Waihi Beach.
Buddy Harwood - For risking his life to save a family of five trapped in a burning car.