Concerns are growing about a West Coast-based gang called Sur 13 moving in on Long Island, and the leader of the Guardian Angels says its members have been seen in several communities.

Sur 13, or Sureno Trece, stands for Southern United Raza.

"They are considered the elite of the gang-bangers," says Guardian Angels founder Curtis Sliwa. "It's like a paramilitary group."

The gang's tattoos and tags are blue with the numerical number 13, representing the 13th letter of the alphabet, "M," which stands for Mexican Mafia.

Sliwa says he first noticed signs of the notorious gang in Corona, Queens about a month ago. He says the gang has most recently been seen in Greenport, Riverhead, Huntington Station, Brentwood and Hempstead. Sliwa adds that Sur 13 -- known for its murders and extortion -- is shaking down undocumented workers for their pay.

Sur 13 is also trying to recruit young Long Islanders in its battle for new turf. Sliwa says the recruits can range from 6 to 12 years old.

Law enforcement expert Denis Monette says local police have been cracking down on the gang with numerous arrests and hefty sentences, but it's hard to keep up with them.

According to Sliwa, MS-13 is the dominant gang on Long Island, but he says Sur 13 is quickly gaining ground because its members are more violent and better organized.