Donald Trump Jr.’s wife, Vanessa Trump, was taken to the hospital Monday after receiving a letter containing white powder that was later deemed to be non-hazardous, New York City police told Fox News.

President Trump's daughter-in-law opened the letter addressed to Donald Trump Jr. just after 10 a.m. at the couple's Manhattan apartment. It's unclear what the "white powder" was, but authorities tested the substance and found it to be "non-hazardous."

Vanessa Trump was taken to the hospital as a precaution, police said. Two other people who were also exposed to the powder were taken to the hospital.

A hazmat crew was called to the scene and began decontamination procedures shortly after the incident.

Trump Jr. tweeted of the "scary situation" on Monday afternoon, and blamed the incident on people with "opposing views."

"Thankful that Vanessa & my children are safe and unharmed after the incredibly scary situation that occurred this morning," Trump Jr. said. "Truly disgusting that certain individuals choose to express their opposing views with such disturbing behavior."

Trump Jr. is the eldest son of the president. He married Vanessa in 2005. The couple has five children, though it was not clear if any were home at the time of the incident.

DONALD TRUMP JR., CONWAY TO END SECRET SERVICE PROTECTION

Police and Secret Service are investigating the incident.

The U.S. Secret Service said in a statement: "The Secret Service and our law enforcement partners in New York City are investigating a suspicious package addressed to one of our protectees received today in New York, New York. This is an active investigation and we cannot comment any further."

Ivanka Trump, Vanessa's sister-in-law, tweeted Monday afternoon, "No one deserves to be frightened this way. There is no excuse."

Trump Jr. ditched his Secret Service detail for a period of time in September, reportedly because he wanted more privacy. But his detail was reactivated about a week later.

Fox News' Nicole Darrah contributed to this report.