NEW YORK — Donald Trump Jr.’s wife was taken to a New York City hospital on Monday as a precaution after she opened an envelope addressed to her husband that contained an unidentified white powder, though police later said the substance wasn’t dangerous, authorities said.

The frightening episode happened after 10 a.m. when Trump, 40, opened the letter addressed to the president’s son at her mother’s midtown Manhattan apartment, investigators said. She called 911 and said she was coughing and felt nauseous, police said.

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

The New York Fire Department said it treated three patients who were then taken to a hospital for evaluation.

Police said the envelope contained a letter but provided no other details.