OMAHA, Neb. (AP) -- Berkshire Hathaway Inc. now holds nearly 12 percent of kidney dialysis firm DaVita Inc. after buying nearly 300,000 more shares.

Warren Buffett's company filed documents with the Securities and Exchange Commission on Friday showing that it owned 11.1 million DaVita shares.

That's up from 10.8 million shares of Denver-based DaVita that Berkshire held one week earlier.

Berkshire has significantly increased its stake in DaVita since it first disclosed owning 2.7 million shares at the end of last year.

Berkshire's regulatory filings don't say whether Buffett himself or one of his company's two other investment managers made the DaVita investment. Berkshire officials don't typically comment on these filings.

DaVita runs nearly 2,000 outpatient dialysis clinics.