Barack Obama's grandmother has started her historic journey from Africa to America to witness her grandson's swearing in as the 44th US President.

Mama Sarah Obama, who will be 87 this year, told US celebrity interviewer Daphne Barak that being the "first grandmother" is hard work.

"I am finding out that to be America's First Grandma is a full time job," she said from her home, a small hut on the shores of Lake Victoria in western Kenya.

Her simple life has changed immeasurably since her step-grandson won the American election.

The potholed road to her village has been fixed, a security fence has been constructed around her house and she even has private security.