More than 400 students and faculty from a Tennessee school have left their classrooms to serenade a teacher suffering from an aggressive form of cancer.

Video of the group singing outside Christ Presbyterian Academy teacher Ben Ellis's home has been viewed more than 24 million times after country star Tim McGraw shared it on his Facebook page.

The video shows Mr Ellis watching the group from a window and singing along.

The Tennessean newspaper reports the unplanned tribute came after students were told Mr Ellis had decided to discontinue treatment for cancer.

The Nashville school classes were stopped and students were taken by bus to Mr Ellis's home.

The father of five said the moment was amazing and made him feel like he "was not alone".