US ethics officials received "an extraordinary volume of contacts from citizens" after a senior adviser to Donald Trump used a TV appearance to endorse Ivanka Trump's line of products.

Ms Conway appeared to be standing inside the White House press briefing room as she made her remarks.

The US Office of Government Ethics said late on Thursday that the "extraordinary" flood of contacts had hit its "website, phone system and email system", and appeared to say it was advising other government agencies on action to take over Ms Conway's statements. Its website crashed due to the high traffic, NPR reported.

On Twitter the office said: "OGE’s website, phone system and email system are receiving an extraordinary volume of contacts from citizens about recent events.

"OGE works to prevent ethics violations. OGE does not have investigative or enforcement authority. Congress, [Government Accountability Office], the FBI, Inspectors General, and the Office of Special Counsel have the authority to conduct investigations.

"When OGE learns of possible ethics violations, OGE contacts the agency, provides guidance & asks them to notify OGE of any action taken. OGE is actively following this agency-contact process."

The office oversees the ethics programme of the US executive branch and advises on law.

During her Fox appearance Ms Conway was discussing Mr Trump's Twitter outburst criticising the retailer Nordstrom, which had dropped his daughter's product line from its shelves. His angry message was also retweeted by the official @POTUS account.

Ms Conway twice praised Ms Trump as a "very successful businesswoman", but that she had "obviously stepped away from it now".