The broadcaster reported that one person had have suffered injured that were not life-threatening.
The New York Police Department posted on its main Twitter account: "The NYPD is responding to reports of an explosion of unknown origin at 42nd Street and 8th Ave, #Manhattan.
"The A, C and E line are being evacuated at this time. Info is preliminary, more when available."
White House Press Secretary Sarah Sanders said President Donald Trump "has been briefed on the explosion in New York City".
The New York Mayor's Office said Mayor Bill de Blasio had also been briefed, adding police and fire crews were on the scene.
Andre Rodriguez, 62, told the New York Times that he heard an explosion shortly before 7.30am.
He added: "I was going through the turnstile. It sounded like an explosion, and everybody started running."
Port Authority is the largest bus terminal in the US, serving more than 65 million passengers a year.
The New York Police Department have confirmed the blast to Sputnik, with no details on reasons behind the incident still unknown at the moment.
The New York Police Department said on Monday that it was responding to reports of an explosion in 42nd Street and 8th Ave in the middle in Manhattan, near the Times Square, one of the most tourist-crowded places in the New York City.
While an evacuation is underway, photos appearing from the site suggest that there is possibly a stampede.
According to eyewitnesses, subway lines are reportedly being evacuated.
The emergency services and law enforcement forces are working at the site, according to photos from the social media.
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