Vanessa Trump arrives on the West Front of the U.S. Capitol on January 20, 2017 in Washington, DC.

Vanessa Trump, President Donald Trump's daughter-in-law, was taken to the hospital Monday after an envelope containing a white powder was sent to her apartment, according to reports.

Three people were hospitalized as a precaution after an envelope was opened that contained white powder and was addressed to Donald Trump Jr., the New York Police Department told CNBC.

Vanessa Trump is married to Donald Trump Jr., the president's eldest son.

The substance, which was not identified, was determined to be nonhazardous after being tested by authorities, the NYPD said. NBC New York, citing a senior official, reported that Vanessa Trump was decontaminated at the scene as a precaution.

At 10:10 a.m., a female called 911 requesting an ambulance, saying she had been exposed to the substance after opening the envelope.

The NYPD's intelligence division, along with hazmat units, EMS services, emergency service units and Secret Service units, responded to the call.

Three people underwent a decontamination process from the hazmat units before being taken to a local area hospital for observation, the NYPD said.

The investigation is still ongoing, White House press secretary Sarah Sanders said on Monday.

"I know the president spoke with her. Beyond that, at this point, it's an ongoing and active investigation so I can't comment any further."

On Monday afternoon, Donald Jr. tweeted that none of his family members involved in the "incredibly scary" situation had been harmed.

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