DETROIT (Reuters) - Automakers have repaired or replaced only one-quarter of the estimated 29 million defective Takata Corp (>> Takata Corporation) air bags in the United States, according to data supplied to U.S. auto safety regulators, with some companies lagging far behind others in terms of completed repairs.

As of March 11, the National Highway Traffic Safety Administration said automakers had replaced more than 7.5 million defective Takata inflators, which can rupture and send hot metal shards into vehicle occupants. The ruptures have been blamed for nine deaths and more than 100 injuries in the United States.

Honda Motor Co (>> Honda Motor Co Ltd), which has been Takata's largest customer, has replaced about 5.4 million inflators - more than half of those it had recalled through December. But the automaker recalled a further 2.3 million defective inflators in February.

Fiat Chrysler Automobiles has replaced 736,000 inflators, about 15 percent of those it recalled, while Toyota Motor Corp (>> Toyota Motor Corp) has replaced 717,000, about 22 percent.

Ford Motor Co (>> Ford Motor Company) has replaced 149,500 inflators, about 21 percent of those it recalled through December, but it recalled 361,692 others in January.

BMW AG (>> Bayerische Motoren Werke AG) has replaced 193,300 inflators, about 21 percent, but the company recalled a further 840,000 in February. BMW has also struggled to complete repairs on driver-side inflators, with a completion rate of less than 2 percent, and recently received an extension from NHTSA.

Some smaller manufacturers, notably Mazda Motor Corp (>> Mazda Motor Corp) and Fuji Heavy Industries' (>> Fuji Heavy Industries Ltd) Subaru, have completed repairs on fewer than 6 percent of their recalled inflators.

NHTSA has mandated that all manufacturers affected by the Takata air bag recalls must have a sufficient supply of replacement parts on hand this year and must complete most of those repairs by the end of 2017.

NHTSA did not respond immediately to a request for comment.

(Reporting by Paul Lienert in Detroit; Editing by Peter Cooney)

By Paul Lienert