Emma Watson was stopped at US immigration because officials thought she was a child.

The 22-year-old actress was stopped at JFK airport in New York where she was questioned by officials at passport control who believed the youthful looking 'Harry Potter' star was an unaccompanied minor.

She tweeted: ''Passport control: 'unaccompanied minor?' Me: 'sorry?' Passport control: 'where is ur guardian?' Me: 'I'm 22!!!!!! #neverwearingbackpackagain

''The really sad thing is that this is not the first time this has happened (sic).''

A source told The People newspaper: ''Emma was mortified. Not only did they not know who she was they thought she was a child. It was very embarrassing but she managed to awkwardly laugh it off.

''The Americans are very serious about who they let in and out of the country. If young kids are thought to be on their own, it poses a massive problem.

''Luckily, Emma managed to convince them how old she is.''

Emma was returning to the US to continue her studies at Brown University in Rhode Island after taking time out to work on film projects.