Blake Lively, left, is Serena and and Leighton Meester is Blair on Gossip Girl. (File photo)

New York City police have stepped in to protect the cast of hit U.S. TV drama Gossip Girl - after fans sparked security fears by storming the set at the weekend.

Co-stars and real-life couple Blake Lively and Penn Badgley, and actors Ed Westwick and Taylor Momsen, were filming a party scene at Manhattan's Empire Hotel when hordes of screaming teen fans prompted complaints from guests.

Police barricades and security guards were needed to keep the over-excited devotees at a distance.

And according to the New York Post, Lively and Badgley's off-screen romance added to the furor.

A source says, "All the people were waiting to get to the rooftop to gawk at them."

Just last month, the cast sparked outrage among residents in the city's quiet Gramercy Park neighbourhood after fans swarmed the set to get a glimpse of guest star Hilary Duff.