After arriving in New York City on a private chartered jet, the newlyweds travelled by limousine for a tour of the site where the World Trade Center once stood.
The royal couple then went Hanover Square to unveil a memorial garden for the 67 Britons who died when the hijacked jets slammed into the Twin Towers.
Charles told the large assembled crowd, "Our hearts go out to you today as they did on that dreadful day...
"Both our nations have been united by grief and strengthened by the support we have given each other."
The tour, designed to celebrate ties between the US and the UK and promote the prince's environmental causes, is the first official overseas trip for the couple since their April (05) wedding.