The terrifying moment two CNN newsreaders were forced to escape a bomb threat live on air.

A bomb threat has forced CNN news anchors Poppy Harlow and Jim Sciutto to evacuate their building live on air.

Crude pipe bombs targeting Hillary Clinton and former president Barack Obama had been intercepted this week. The pair were delivering this news around 10am Wednednesday local time (1am Thursday Australian east coast time) when they heard an alarm go off in their building and learned they themselves may be in danger.

The newsreaders looked wide-eyed, but tried to push on with their broadcast before they were eventually forced to cut it short.

“There is a fire alarm here … we’ll be right back,” Sciutto said.

Watch the moment the CNN team are evacuated:

According to CNN, the building was forced to evacuate after authorities discovered a package containing a bomb. It did not detonate.

It comes two weeks before nationwide elections that could reshape US Congress and serve as a referendum on the first two years of President Donald Trump’s presidency.

The devices, which officials said shared a similar design, were aimed at prominent Democrats and a cable news network often criticised by political conservatives. A similar device was found Monday at the New York compound of liberal billionaire George Soros, a major contributor to Democratic causes.

The bombs overtook other campaign news in an already-tense political season, which has included pitched fights over immigration, the Supreme Court and sexual violence against women.

The White House quickly condemned the attacks aimed at Democrats and perceived foes of the administration.

“Acts or threats of political violence have no place in the United States,” Trump said.

“This egregious conduct is abhorrent.”

“That’s a very bipartisan statement,” he said.

All the confirmed bombs appeared to come from the same person or persons, said John Miller, the New York Police Department’s head of intelligence and counterterrorism, who briefed reporters in New York.

The US Secret Service intercepted a bomb that was addressed to Hillary Clinton at the Chappaqua, New York, home she shares with former President Bill Clinton, and another that was sent to former President Obama at his home with Michelle Obama in Washington. A police bomb squad removed still another from CNN’s New York headquarters, which was evacuated.

“We will not rest until we stop these hazardous devices from being mailed and bring the individual or individuals to justice,” said Bryan Paarmann, the FBI’s top counterterrorism official in New York.

The FBI also said it was responding to a report of a suspicious package at a Florida office of Representative Deborah Wasserman Schultz. New York Governor Andrew Cuomo said his office received a similar package, but New York police officials said the office was cleared and no device was found.

Cuomo said at a briefing that “we will not allow these terrorist thugs to change the way we live our lives.”

Neither Clinton nor Obama received the packages, and neither was at risk of receiving them because of screening procedures, the Secret Service said.

White House press secretary Sarah Sanders said in a statement, “These terrorizing acts are despicable, and anyone responsible will be held accountable to the fullest extent of the law.”

Two law enforcement officials, speaking to AP on condition of anonymity to discuss an ongoing investigation, said the pipe bomb at CNN was crude but operational and was addressed to former CIA Director John Brennan, who regularly appears as a television contributor and who has publicly clashed with Trump. They said it was similar to other explosives discovered in the past few days.

A law enforcement official told the AP that the package discovered at Soros’ home appeared to be a pipe bomb and was in a package placed in a mailbox outside the gates of the compound. A Soros employee opened it just inside the gates, not near Soros’ quarters, the official said.