A woman and her grandson held on to a big red cross for five hours as they were trapped in raging floodwaters in South Carolina Sunday before they were rescued.

Clara Gantt told NBC station WIS that at around 6 a.m., she drove her car to attend service at the Three Rivers Baptist Church in Irmo despite the incessant rains.

Because it was still dark and visibility was poor because of the rains, she underestimated the height of the flood which swept her car away.

"I knew there was water out there, but I didn't know that it was going to stall me and it did," said Gantt, according to NBC News.

Her car ended up on a field next to a small church. She attempted to call 911 but got no answer but she eventually reached her family. She was finally able to get in touch with her family.

At that point she said to herself, "Dear Lord are you taking me home right now?"

But then when she flipped over to her back she heard a voice inside her head, saying, "No, not right now."

Her grandson, Travis Catchings, came to her rescue. He carried a deer harness and some rope. He was able to reach his grandmother, whose car had been washed off the road into a church yard at Jordan Independent Church. "I got [the door] open and got her out of the car," Catchings said. "At that point we had to just sit there and wait," he added, realising that both of them were now trapped in the flood.

"There was a little church right there. Where my car stopped was right beside a huge red cross," Gantt said. "I was literally, after I got out of the car, holding onto the cross. I was clinging to the cross."

Gantt and her grandson both held on to a bright red cross until the rescuers arrived.

Catchings said he was already feeling hopeless that they would be rescued on time since the floodwater was rising fast, so he made his last phone call to his wife.

"I really thought that was the last time that I was ever going to talk to her. I thought that was the last time that I'd ever going to hear her voice," he said. "It was the hardest phone call I've ever made. And I just told her that I loved her, and I didn't know what was going to happen."

He added, "Jesus is my saviour. This story is not about me, it's about what He did to save me. And He set my feet on higher ground."

Gantt suffered a broken ankle because of the incident.

At least 17 people were killed in the South Carolina floods.