Republican John McCain virtually sealed his nomination, leaving one-time frontrunner Mitt Romney's campaign in shambles. The 72-year-old Vietnam veteran grabbed California, where Romney was hoping to turn the tide after losing several key states to McCain and Mike Huckabee, who revived his campaign with victories in Georgia, Tennessee and Alabama.

The two Democratic rivals who are locked in a tight and bitter contest poached into each other's territories in the biggest primary day in US history setting the stage for a long fight for the party's nomination.

Clinton, seeking to become the first woman President of the United States, won the biggest prize, California, with a strong showing among Hispanics and Asian Americans, and Massachusetts where she battled the powerful Kennedy clan.

Obama, 46, who has won several high-profile endorsements, bagged 13 states against Clinton's eight showing off his mass appeal in the coast-to coast contest.

He won the deep south states of Georgia and Alabama, posted east coast victories in Connecticut and Delaware, consolidated in the mid-west with Minnesota, Kansas, Utah and North Dakota. He sewed up easy wins in his home state of Illinois and the western state of Colorado. He also won Alaska, Idaho and Missouri.