Donald Trump Jr’s wife has been admitted to hospital after opening a letter at her home that contained an unknown white powder, police said.

Vanessa Trump, 40, was examined at a New York hospital on Monday (US time) as a precaution, before the substance was determined not to be hazardous.

“The substance had arrived by mail and it was addressed to Donald Trump Jr,” New York Police Department spokesman Carlos Nieves said.

The daughter-in-law of President Donald Trump was hospitalised after she complained of nausea after her exposure, New York Police stated.

Emergency services were called to Mr Trump Jr’s Manhattan apartment at 10am after his wife opened the letter.

Vanessa Trump was taken to New York-Presbyterian Weill Cornell Medical Centre as a precaution. Photo: Getty

Three other patients from the home, including Mrs Trump’s mother, were transported to the New York-Presbyterian Weill Cornell Centre for further evaluation.

According to Reuters, US authorities have been on high alert over mail containing white powder in it since 2001, when envelopes laced with anthrax were sent to media outlets and US politicians, killing five people.

However, New York Police analysis found the substance to be harmless. US media reports say the white powder turned out to be cornstarch.

“The substance was deemed to be nonhazardous and is being transported to a lab in New York City for further analysis,” NYPD spokesman Peter J. Donald said.

The US Secret Service – which is in charge of protecting the President’s family members – is also investigating.

“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,” the Secret Service said in a statement.

White House officials are yet to comment on the matter.

– with wires