Los Angeles: California Attorney General Kamala Harris—the first woman and the first minority to hold that office—will seek the U.S. Senate seat being vacated by Sen. Barbara Boxer, an adviser with knowledge of her plans said on Monday.

With her formal announcement on Tuesday, Harris, 50, would become the first California Democrat to enter the 2016 race expected to lure a crowded field.

The adviser was not authorized to discuss Harris's plans and spoke only on the condition of anonymity.

Harris, a former two-term San Francisco district attorney, is a personal friend of President Barack Obama and attracted national attention when she helped negotiate a settlement with major mortgage lenders and secured extra funding for California. She has been widely viewed as an eventual candidate for governor or U.S. senator.

The disclosure of her plans came shortly after a potential rival, California Lt. Gov. Gavin Newsom, who served eight years as mayor of San Francisco, said he would not run for the open seat created by Boxer's retirement next year. His statement did nothing to dampen the idea he would run for governor in 2018 -- when the term of current Gov. Jerry Brown ends.

Former Los Angeles Mayor Antonio Villaraigosa and Tom Steyer, a retired San Francisco hedge fund billionaire who sought to make climate change an issue in the November elections, are also considering bids for the seat, which Boxer has held for over two decades. Democrats are well positioned to retain the seat in a state where the party controls every statewide office and both chambers in the Legislature.

As the state's chief law enforcement officer, Harris has focused her crime-fighting efforts on cross-border gangs that she says are increasingly engaged in high-tech crimes such as digital piracy and computer hacking to target businesses and financial institutions.

In 2010, Harris was elected California attorney general. She is the daughter of an Indian mother and black father.