By Michael Erman

(Reuters) -Swiss drugmaker Roche Holding AG plans to sell its 800-employee drug manufacturing plant in Vacaville, California, or it will shut the factory by 2029, according to e-mailed letters to workers seen by Reuters on Wednesday.

Roche confirmed the divestiture plan in a statement, but did not address the potential closing of the plant or its timeline.

The company said it does not expect to need the very large volumes of the medicines the plant provides, and large-scale production will be done in one of the company's newer plants. It also plans to focus on drugs targeting smaller patient populations moving forward, it said in the emails to employees.

According to Roche, there will be no impact to operations or employees at this time.

Roche is under new leadership this year after CEO Thomas Schinecker took the helm and Theresa Graham became head of the pharmaceuticals division in March. It is contending with dipping revenue for its COVID-19 therapies and tests.

The company said it is seeking a buyer that will continue to use the plant as an operating facility.

If the company is unable to find a buyer, it will ramp down production and close the plant in 2028 to 2029, the emails said.

Roche acquired the plant more than a decade ago with its purchase of U.S. biotech Genentech. The plant makes drugs for cancer including Avastin and Herceptin, as well as Actemra for rheumatoid arthritis.

During the pandemic, Roche collaborated with Regeneron Pharmaceuticals to increase supply of that drugmaker's COVID-19 antibody treatment. Roche manufactured the treatment at the Vacaville plant, which it sells outside the U.S. under the brand name Ronapreve.

(Reporting by Michael ErmanEditing by Diane Craft and Bill Berkrot)