UPDATE: An explosion occurred during rush hour Monday morning near New York City's Port Authority, police said.

One suspect was in custody following the incident at 42nd Street and Eighth Avenue, according to a senior NYPD official.

The Fire Department of New York said there was a total of four non-life-threatening injuries. Earlier, law enforcement officials told NBC News the suspect was the only person hurt and sustained a minor injury.

Three law enforcement officials said that the explosion was believed to be an "intentional act." The suspect had some sort of pipe bomb or other type of improvised explosive device that either went off prematurely or only partially detonated, the law enforcement officials said.

A federal law enforcement official said the man was wearing the explosive device. Officials don't know if it was a backpack, vest, or belt.

NYPD and FBI are investigating whether it was a lone actor with a lone incendiary device, or whether it was part of a broader plot. The FBI's Joint Terrorism Task Force is also involved in the probe.

Former NYPD commissioner Bill Bratton said preliminary information indicated that the explosion was carried out by a man in his mid-20s who detonated the device in the name of ISIS.

"The preliminary information from three sources, and I emphasize my former word, preliminary, subject to change: It is a man in his middle 20s probably, possibly from Bangladesh. Been in the country about seven years, who was supposedly setting the device off in the name of ISIS. So definitely a terrorist attack, definitely intended," Bratton told MSNBC.

"As to whether the device malfunctioned or didn’t function correctly, that’ll have to be determined," Bratton added.

The incident, in the heart of the city, caused chaos for morning commuters. Emergency vehicles that stretched for blocks rushed to the scene, causing major evacuations in the massive transit hub. Subway lines were thrown into disarray, with at least 10 bypassing the Times Square and 42nd Street/Port Authority stops.

Two students who were about to swipe into the subway said that they were trying to get to school when the explosion went off.

"I was about to swipe in my card and out of nowhere, we heard a really loud bang, everyone said 'get out, get out!'" Ali, 18, who declined to give his last name, said.

His friend, Saidou Choudhury, 19, said the explosion "sounded like it was deep inside."

"I was traumatized," he said.

Another commuter, Isham Chowdhury, was on a bus bound for Port Authority when the explosion went off. He said he got to the terminal about 10 minutes afterwards.

"They were closing the entrance due to the attack. Everyone was calm, but we knew it wasn't normal," Chowdhury said. "The escalators were shut."

The FDNY said they received a call about the explosion at 7:19 a.m. ET.

The incident comes a mere six weeks after a truck driver deliberately drove down a bike path in lower Manhattan, killing eight people in the deadliest terror attack in New York City since Sept. 11, 2001.

The Port Authority Bus Terminal is the nation's largest bus terminal, with about 230,000 passengers passing through it on a typical weekday, its website says.

President Donald Trump was briefed on the incident, White House spokeswoman Sarah Huckabee Sanders said.

This is a developing story. Check back for updates.