Authorities believe the white powdery substance was probably cornstarch. It was postmarked from Boston.
Realising the potential danger, a panicked Mrs Trump then ran out of the room and stashed the letter and powder in a plastic bag and called 911, sources said.More news: Get Out is returning to theaters for free on President's Day
Officials said she did not suffer any ill effects and was decontaminated at the scene. The powder remains at a lab in the city for further testing, officials said.
"Thinking of [Vanessa Trump] & wishing I was by her side today", Ivanka Trump wrote. "Thank you @FDNY @SecretService @NYPDnews @NYPDCT @NewYorkFBI". "Truly disgusting that certain individuals choose to express their opposing views with such disturbing behavior".
The president hasn't commented on the episode. The Associated Press reported that she was coughing and feeling nauseated.More news: Magic Leap unveils partnership with National Basketball Association for mixed reality app
Trump Jr. has been a target of criticism for his role in a 2016 meeting with a group of Russians at New York's Trump Tower. The 40-year-old politician, Trump Junior, took to social media to update his fans the very same day in an Instagram and Twitter post that we have for you above.
Mrs Trump's five children were not home at the time.More news: Sam's Club reduces membership categories, offers more free shipping
The written contents of an envelope containing a white powder received Monday by Donald Trump Jr.'s wife said the president's son would get what he "deserves", the NYPD confirmed to Fox News on Tuesday.