New York, New York - Brian Thompson, the chief executive of health insurance giant UnitedHealthcare, was shot and killed outside a New York Hilton hotel in an apparently targeted hit Wednesday.

Multiple outlets reported that the 50-year-old was shot just before 7 AM outside the Hilton Hotel in Midtown Manhattan, with CNBC citing a source who said a silencer had been used in what was described as a "targeted attack."

The gunman, described as wearing a black face mask, then fled following the incident, which is expected to spark a manhunt.

Police confirmed a shooting at the location as officers swarmed around the area around the hotel, a usually busy corner of Manhattan that would have been filled with commuters at the time of the shooting.

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UnitedHealth Group, the parent company of UHC, is one of the biggest health insurance companies in the US, posting revenues of $100.8 billion in the third quarter of the year.

UnitedHealthcare's Employer and Individual products are used by almost 30 million people in the US, according to an investor presentation.

The company was due to hold an investor day in New York Wednesday, with Thompson scheduled to deliver a keynote speech. The event has been canceled.

A manhunt is underway for the gunman who shot Thompson on Wednesday morning.

Police have released security camera images showing the killer brandishing a handgun and wearing a hooded top, and detectives are offering a $10,000 reward for the man's capture.

Chief of Detectives Joseph Kenny said the shooter arrived on foot about five minutes before Thompson as pedestrians streamed past an access door to the Hilton.

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Kenny said he approached Thompson from behind and opened fire, cleared a jam in the firearm, and fired again.

"The motive for this murder currently is unknown, but based on the evidence we have so far, it does appear that the victim was specifically targeted. But at this point, we do not know why," Kenny told a press conference.

The detective had no comment when asked at the press conference whether the killing could have been carried out by someone who had been denied insurance coverage for a medical condition.

Minnesota-based Thompson's wife Paulette Thompson told the NBC News outlet that he had received unspecified threats.

"There had been some threats basically, I don't know – [over] a lack of coverage? I don't know details," said Paulette Thompson, who had two children with her late husband.

In a statement, UnitedHealth Group – the parent company of UHC – said it was "deeply saddened and shocked."

Officers said the lighting of the Christmas tree at the nearby Rockefeller Center, a major annual event that draws vast crowds of tourists and locals, would proceed normally amid tightened security.