Eleven years later, NYPD have discovered a piece of plane wreckage thought to be landing gear. Fox News/myfoxny.com

A 1.5 METRE-tall piece of landing gear believed to be from one of the planes that hit the World Trade Center in the September 11 terror attacks has been discovered wedged between a mosque site and another building near ground zero.

The part includes a clearly visible Boeing identification number, New York Police Department spokesman Paul Browne said today.

The twisted, rusted metal part has cables and levers on it and is about 0.9 metres wide and 0.5 metres tall.

An NYPD photo shows the gear was found in a narrow gap between the two buildings.

The gap appears to be barely wide enough for a person to walk through.

''The way it was wedged, it had to go in just the right way for it to go undetected for over a decade,'' Browne said.

The site is being treated as a crime scene, police said

The medical examiner's office will complete a health and safety evaluation to determine whether to sift the soil around the buildings for possible human remains, police said.

The aircraft part will not be removed until evaluations are done and then it will be kept by the NYPD, Browne said.

The piece of equipment was discovered on Wednesday by surveyors inspecting the lower Manhattan site of a planned Islamic community centre, at 51 Park Place, on behalf of the building's owner, police said.

The inspectors called police who secured the scene, documenting it with photos.

The spot where the landing gear was found is about three blocks from ground zero.

When plans for the mosque and community centre were first announced several years ago, opponents protested that putting a Muslim facility near ground zero showed disrespect.

Supporters cited freedom of religion and said it wasn't too close to where Islamic extremists attacked on September 11, 2001.

Two hijacked planes slammed into the nearby World Trade Center towers in 2001, killing thousands of people.

Where the landing gear was found: