By German Dam

PUERTO ORDAZ, Venezuela, (Reuters) - At least 14people were killed Monday when a plane owned by Venezuela'sstate-run airline Conviasa with 51 people on board slammed intothe yard of a steel mill, officials said.

Four on board were reported missing.

The ATR-42 plane was on a domestic route between theCaribbean island of Margarita and the southern industrial cityPuerto Ordaz when it came down near the gates of the vast Sidormill on the banks of the Orinoco river.

Workers and firemen from the plant ran to the crash siteand pulled passengers from the twisted and charred wreckage,one steel worker told state television.

"So far 33 people are being treated in nearby clinics andhospitals. Sadly we have 14 bodies to identify and we have notfound four people," local governor Francisco Rangel Gomezsaid.

Images showed the fuselage broken into at least two piecesin a yard stacked with junk and empty barrels. The wings layseveral meters away.

A nearby Puerto Ordaz hospital received injured people andbodies from the crash site. Hospital director Yanitza Rodriguezsaid many of the injuries were serious.

An official at the National Civil Aviation Institute saidthe pilot had radioed in a mayday signal seconds before theplane crashed.

"We presume (the accident) was caused by a failure in theairplane's controls," said the official, who asked not to beidentified.

ATR, which makes 40-70 seat twin-engined turboprops, is ajoint venture between Airbus parent company EADS and Italianaerospace group Finmeccanica.

President Hugo Chavez created Conviasa in 2004 to replaceVenezuela's bankrupted flagship airline Viasa.

Officials said the crash did not cause any injuries tosteel workers or damage to Sidor's installations.

"The plane fell on a waste area where they put barrels ofunused steel materials," governor Gomez said.

In the last major crash in Venezuela in 2008, anotherATR-42 belonging to private local airline Santa Barbara with 46passengers on board crashed into mountains, with no survivors.

The Conviasa plane was flying flight number 2350 andcarried the registration YV1010. (Additional reporting by Eyanir Chinea, Frank Jack Daniel,Diego Ore, Marianna Parraga in Caracas: Editing by AndrewCawthorne and Jerry Norton)