Zohran Mamdani, the Democratic nominee for New York mayor, has posted on social media about the attack.

"I’m heartbroken to learn of the horrific shooting in midtown and I am holding the victims, their families, and the NYPD officer in critical condition in my thoughts," he wrote on X.

"Grateful for all of our first responders on the ground."

The attack took place while the candidate was visiting family members in Uganda, according to the New York Times.

A surveillance camera has captured an image of the suspected gunman, as the BBC's US media partner CBS news has reported.

He could be seen walking, weapon in hand, towards a series of double doors - wearing sunglasses.

The security footage is labelled as belonging to 345 Park Avenue.

Police have not confirmed the identity of the suspect. Earlier, CBS reported that the lone shooter was dead.

Image source, CBS News New York

Lawmakers from New York have been posting their messages on social media.

House Minority Leader Hakeem Jeffries, the top Democrat in Congress who represents part of New York City in the House of Representatives, posted on X that he is "deeply disturbed" by the shooting.

"Praying hard for the brave NYPD officer impacted and all other victims of this tragedy," Jeffries wrote.

Congressman Ritchie Torres called the attack a "shocking act of terror".

He called it "a grim reminder of the persistent danger posed by firearms, the hardening of hatred in our society, and the exceptional courage of the NYPD officers who risk their lives in order to protect the rest of us".

New York Senator Chuck Schumer thanked "our brave first responders on the scene in Manhattan tonight."

"I’m praying for everyone affected. We must do more to stop gun violence in America."

New York Mayor Eric Adams, who has been on the scene, says "multiple people" have been injured in the shooting.

In a video posted online, Adams says people inside the office complex should "remain inside as police officers are doing a floor by floor search."

"We will going over to the hospital to speak with family and love ones" of those impacted by the incident, he says.

A police officer was fatally shot, according to CBS News, the BBC's US partner, citing two law enforcement sources.

CBS reports that two NYPD officers, who were off-duty but working as security in the building, and two civilians were shot.

One officer has died in the incident and one of the civilians was listed in critical condition, sources told the network.

Police have not confirmed that an officer has died.

The exact location of the shooting is still unknown. But based on the police response, it appears that the shots took place in a building that houses offices for the National Football League (NFL), investment firm Blackstone, and numerous other businesses.

The building in Midtown Manhattan, 345 Park Avenue, takes up an entire city block and is large enough to have its own postal code – known in the US as a zip code.

The building was built in 1969, has 44 floors, and is 1,900,000 sq ft, according to Rudin real estate, which owns the building and hosts its headquarters there.

For those unfamiliar with New York City, Park Avenue in midtown East Manhattan is a cornerstone of the city's most prestigious corridor. Just a few blocks south of Central Park, the area where the attack took place contains several of the city's massive and iconic skyscrapers.

The New York Police Department is now confirming that the "lone shooter" who attacked an office building in Manhattan is dead.

The attacker died from a self-inflicted gunshot wound, according to CBS News, the BBC's US partner.

Police have not yet confirmed how they died, with the commissioner writing earlier that they had been "neutralized".

The scene is now "contained", the NYPD statement adds, telling people to continue to avoid the area.

Indrani Basu
BBC News, New York

Bystanders heard a loud bang and began running down Lexington Avenue. I saw a man being handcuffed and taken away - and NYPD officer on the scene confirmed there has been an arrest and that one other person was at large.

It's unclear whether the arrest was tied to the shots-fired call.

All trains have been shut down in the area.

Four blocks around the intersection are also closed off for general public.

NYPD officers won't say if there has been a second arrest and they are asking people to leave the area for their safety.

New York Police Department Commissioner Jessica Tisch has just posted a one-sentence update.

"UPDATE: At this time, the scene has been contained and the lone shooter has been neutralized," she wrote on X, without adding further detail.

A heavy police presence remains at the scene.

The FBI has dispatched agents to help local police according to the agency's deputy director Dan Bongino.

"New York Field Office management personnel and agents are responding to provide support at the active crime scene in Manhattan," Bongino says in an X post.

Indrani Basu
BBC News, New York

At around 6:45pm local time (11:45pm BST) I saw about three NYPD cars and two FDNY trucks at the intersection of Lexington Avenue and 51st Street.

A man was being wheeled away in a stretcher with bandages strapped to his chest. A bystander told me that he heard about half a dozen gunshots.

The NYPD officers at the scene confirmed that there was an active shooter in the area and likely at a building a block west of the intersection at a bank.

Authorities are responding to a call of shots fired in a Midtown Manhattan office building, police told the BBC.

A BBC News editor is near the scene. She reported seeing scores of police vehicles and at least one person with a bloodied chest being taken away.

It is unclear how or where they were injured.

The New York City Police Department responded to the call at 345 Park Avenue on Monday evening.

A man near the scene was also seen being placed in handcuffs by police, though it's unclear whether he was involved in the incident.

New York police urged the public to avoid the area.

We will bring you the live updates on the ground. Stay with us.