Sarah Thomas completed treatment for cancer a year ago.

An American breast cancer survivor on Tuesday became the first person to swim across the Channel four times non-stop in a 54-hour feat of endurance.

Sarah Thomas, 37, could be seen in a video posted on Facebook arriving at Dover on the southern English coast with a group of supporters cheering her on.

"I feel a little sick," she is heard saying in the video.

In a post on Saturday before setting off, Thomas wrote: "This swim is dedicated to all the survivors out there.

"This is for those of us who have prayed for our lives, who have wondered with despair about what comes next, and have battled through pain and fear to overcome," she wrote.

Thomas completed treatment for cancer a year ago.

Thomas told the BBC the hardest part of the swim was dealing with the salt water, which left her throat and mouth sore. She said she also got stung in the face by a jellyfish.

Endurance swimmer Lewis Pugh wrote on Twitter that her achievement was "extraordinary, amazing, super-human".

"Just when we think we've reached the limit of human endurance, someone shatters the records," he wrote.