Hillary Clinton today made history as she became the first woman to clinch the presidential nomination of a major American political party by winning crucial California and three other state primaries but her Democratic rival Bernie Sanders remained defiant.

"Thanks to you, we've reached a milestone, the first time in our nation's history that a woman will be a major party's nominee," Clinton, 68, told her supporters at her campaign headquarters in Brooklyn, New York. President Barack Obama congratulated Clinton for securing the 2,383 delegates necessary to clinch the Democratic party's presidential nomination.

However, Obama did not formally endorse Clinton -- his former Secretary of State. "Her historic campaign inspired millions and is an extension of her lifelong fight for middle-class families and children," White House Press Secretary Josh Earnest said. Obama called both Clinton and Sanders to applaud them for "running inspiring campaigns that energised Democrats."

The President will meet Sanders at the White House tomorrow at the Vermont senator's request, Earnest said in a statement.