The Russian ambassador to the United Nations died after suffering cardiac arrest in Manhattan Monday morning, a day before his 65th birthday, sources told The Post.

Vitaly Churkin fell ill at his office at the Russian Mission to the U.N. on East 67th Street around 9:30 a.m. and was unconscious when emergency personnel arrived, sources said.

Churkin was given CPR and taken to New York Presbyterian Hospital in serious condition.

He was pronounced dead at 10:55 a.m., sources added.

Churkin had served as Russia’s permanent representative to the U.N. since 2006.

His death was announced Monday, followed by a moment of silence, at a routine meeting on General Assembly matters.

Many of Churkin’s colleagues took to social media to express their condolences.

“Shocked and saddened to learn that Ambassador Vitaly Churkin passed away. A top diplomat and a good friend,” Russian Ambassador to the UK Alexander Yakovenko tweeted.

Netherlands’ UN Ambassador Karel van Oosterom wrote: “Emotional announcement at UN of passing away this morning of PermRep Russia Churkin and moment of commemoration and condolences.”

The Russian Foreign Ministry confirmed Churkin “unexpectedly died” but provided no details as to how he died.

It called him an “outstanding” envoy.

Spokeswoman Maria Zakharova said in a Facebook post that Churkin was “an extraordinary person. A bright man. We have lost a dear one.”

President Vladimir Putin was notified of his death, state news agency TASS reported.

“The president was grieved to learn about the death of Vitaly Churkin. The head of state highly estimated Churkin’s professionalism and diplomatic talents,” spokesman Dmitry Peskov said, according to the agency.

Churkin was currently the longest-serving member of the Security Council, the UN’s most powerful body.

“He has been such a regular presence here that I am actually quite stunned. Our thoughts go to his family, to his friends and to his government,” said Farhan Haq, a spokesman for the UN secretary-general’s office.

Churkin was a staunch supporter of Russian policy, including its bombing of Aleppo in Syria last year.

He slammed US Ambassador Samantha Power for acting like “Mother Teresa” – while noting America’s track record in the Middle East — after she lambasted Russia, Syria and Iran over the Aleppo crisis.

Power also reacted to Churkin’s sudden death.

“Devastated by passing of Russian UN Amb Vitaly Churkin.Diplomatic maestro &deeply caring man who did all he cld to bridge US-RUS differences,” she tweeted.

US Ambassador to the UN Nikki Haley, who earlier this month blamed Russia for the spike in violence in eastern Ukraine and said sanctions wouldn’t be lifted until Moscow returned Crimea to Kiev, issued a statement calling Churkin “a gracious colleague.”

“We did not always see things the same way, but he unquestionably advocated his country’s positions with great skill,” she said. “We send our prayers and heartfelt condolences to lift up his family and to the Russian people.”

Churkin previously worked in the foreign ministry in Moscow.

Additional reporting by Gina Daidone and Post Wires