WASHINGTON -- The world is not coming to an end on December 21, 2012, the US space agency insisted Monday in a rare campaign to dispel widespread rumors fuelled by the Internet and a new Hollywood movie.

Sony Pictures's latest big screen offering "2012" arrives in theaters on Friday, with a $200-million production about the end of the world supposedly based on myths backed by the Mayan calendar.

The doomsday scenario revolves on claims that the end of time will come as an obscure Planet X -- or Nibiru -- heads toward or collides into Earth.

The mysterious planet was supposedly discovered by the Sumerians, according to claims by pseudo-scientists, paranormal activity enthusiasts and Internet theorists.

Some websites accuse NASA of concealing the truth on the wayward planet's existence, but the US space agency denounced such stories as an "Internet hoax."

"There is no factual basis for these claims," NASA said in a question-and-answer posting on its website.

If such a collision were real "astronomers would have been tracking it for at least the past decade, and it would be visible by now to the naked eye," it added. "Obviously, it does not exist."

"Credible scientists worldwide know of no threat associated with 2012," NASA insisted.

Initial theories set the disaster for May 2003, but when nothing happened the date was moved forward to the winter solstice in 2012 to coincide with the end of a cycle of the ancient Mayan calendar.

But NASA insisted the Mayan calendar in fact does not end on December 21, 2012, as another period begins immediately afterward. And it said there are no planetary alignments on the horizon for the next few decades.

And even if the planets were to line up as some have forecast, the effect on our planet would be "negligible," NASA said.

Among the other theories NASA has set out to debunk are that geomagnetic storms, a pole reversal or unsteadiness in the Earth's crustal plates might befall the planet.

And while comets and asteroids have always hit the Earth, "big hits are very rare," NASA noted. The last major impact was believed to be 65 million years ago, spurring the end of dinosaurs.

"We have already determined that there are no threatening asteroids as large as the one that killed the dinosaurs," the space agency said.