Suspicious packages, identified as potential explosives, addressed to former president Barack Obama and defeated presidential nominee Hillary Clinton have been intercepted by the Secret Service, officials said Wednesday.

The Secret Service said it recovered a single package addressed to Clinton in Westchester, a suburb north of Manhattan on Tuesday, and a second package addressed to the Obama residence in Washington on Wednesday.

Both Democrats remain two of the most high-profile political figures in the United States, which goes to the polls on November 6 in key midterm elections seen as a referendum on Republican President Donald Trump.

The White House swiftly condemned what it called "despicable" acts targeting the two Democrat luminaries.

"The packages were immediately identified during routine mail screening procedures as potential explosive devices and were appropriately handled as such," the Secret Service said in a statement.

"The protectees did not receive the packages nor were they at risk of receiving them."

Moments later US news network CNN said it had evacuated its New York bureau over another suspicious package.

New York police confirmed to AFP that its officers had been called to the Time Warner Center, where the CNN bureau in the US financial capital is located, to investigate reports of a suspicious package.

The Secret Service, which provides protection to current and former US presidents and their families -- Clinton is the wife of former president Bill Clinton -- said it had initiated a "full scope criminal investigation."

The investigation would "leverage all available federal, state, and local resources" to determine the source of the packages and identify those responsible, it said.

It was not immediately clear whether Clinton or Obama, who has kept a family base in Washington after leaving office so that his youngest daughter can finish high school, were at home when the packages were found.

- Target for right-wingers -
The FBI's field office in New York said it was "aware" of a suspicious package found in the vicinity" of Clinton's home in Chappaqua and that its Joint Terrorism Task Force was investigating.

The incidents come just days after an explosive device found in the mailbox at the New York home of US billionaire and liberal donor George Soros, a target of right-wing groups.

An employee of the residence in Bedford, an ultra-wealthy enclave just a 20-minute drive from Westchester, found the package in the mailbox on Monday. It was later defused by bomb squad technicians.

Born in Hungary, the 88-year-old hedge fund tycoon is one of the world's richest men with an estimated net worth of $8.3 billion and a prominent philanthropist who has become a hate figure for right-wing groups.

Soros supported Clinton, Trump's rival in the 2016 US presidential election, and has been accused by nationalists the world over of sponsoring protests and seeking to push a liberal, multicultural agenda.

His Open Society Foundations on Tuesday condemned the "hateful rhetoric that dominates politics in the United States and so many countries around the world," noting it "breeds extremism and violence.

"In this climate of fear, falsehoods, and rising authoritarianism, just voicing your views can draw death threats," it said.

Earlier this month Trump accused Soros of paying demonstrators to protest against the nomination of Supreme Court Justice Brett Kavanaugh, who was accused of attempted rape in high school.

Soros has also been falsely accused of funding the caravan of migrants moving north from Honduras through Mexico en route to the US border. (AFP)

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