US President Donald Trump's daughter-in-law has thanked emergency services after she was taken to hospital when she received a suspicious letter containing white powder.
Vanessa Trump, the wife of Donald Trump Jr, was hospitalised after telling police she had been exposed to white powder after opening an envelope, which was later determined as non-hazardous.
She later tweeted that she was grateful to the New York City Fire Department, the Secret Service, the New York City Police Department and the FBI.
"I appreciate all the quick response to make sure that I was safe [sic]," she wrote.
Two other people who were present when she opened the envelope were also taken to the hospital.
"The substance had arrived by mail and it was addressed to Donald Trump Jr.," said New York Police Department spokesman Carlos Nieves.
Three patients from the household were transported to hospital for further evaluation, said Fire Department spokeswoman Sophia Kim.
The three included Vanessa Trump's mother, although she had not complained of symptoms, the police spokesman said.
The package had a Boston postmark, ABC News and the New York Post reported.
"Thankful that Vanessa & my children are safe and unharmed after the incredibly scary situation that occurred this morning," Trump Jr. said on Twitter.
"Truly disgusting that certain individuals choose to express their opposing views with such disturbing behaviour."
Ivanka Trump, the president's daughter and Vanessa Trump's sister-in-law, also messaged her support.
"Thinking of @MrsVanessaTrump & wishing I was by her side today. No one deserves to be frightened this way. There is no excuse," she wrote on Twitter.
The Secret Service, which is charged with protecting members of the president's family, confirmed it was involved in the investigation, said spokesman Jeffrey Adams.
Trump Jr in September briefly gave up his Secret Service protection, normally provided to the immediate families of all sitting presidents, the New York Times reported at the time.
His protective detail was restored after about a week, CNN reported.
Trump Jr has been in the public eye for his role in a 2016 meeting with a Russian lawyer and others after the Trump campaign was offered potentially damaging information about Democratic rival Hillary Clinton.
Congress has held probes into that meeting and whether it was part of a Russian campaign to influence the 2016 presidential election, which both Russia and Trump deny.