WASHINGTON (REUTERS) - US President Donald Trump visited his younger brother Robert in a New York City hospital for about 45 minutes on Friday (Aug 14), before heading for his New Jersey country club where he planned to spend the night.

Trump told a news conference prior to the visit that his brother was in the hospital, but he did not elaborate on the reason.

"I have a wonderful brother. We've had a great relationship for a long time, from day one," Trump said.

"Hopefully, he'll be all right, but he's having a hard time."

ABC News said Robert Trump was "very ill," citing unidentified sources.

Following the visit to New York-Presbyterian/Weill Cornell Medical Centre on the Upper East Side of Manhattan, in which he wore a mask, Trump was due to deliver remarks to the City of New York Police Benevolent Association in Bedminster, New Jersey, where he would spend the night at his country club.

ABC reported that Robert Trump was hospitalised in the intensive care unit at Mount Sinai hospital in New York for more than a week in June.

That same month, Robert Trump won a temporary restraining order against his niece, Mary Trump, to stop her from publishing a tell-all book that offers an unflattering look of the US president and his family.

A state supreme court judge in Poughkeepsie, New York, later denied a request to stop publication and cancelled the temporary restraining order.

Robert Trump had said the book Too Much And Never Enough: How My Family Created The World's Most Dangerous Man would violate a confidentiality agreement tied to the estate of his father Fred Trump Sr, who died in 1999.