Pharmaceutical giant GlaxoSmithKline has shut down a US plant that produces inhaled medications after discovering the bacteria that causes Legionnaires' disease.

The manufacturing plant in Zebulon, about 25 miles east of Raleigh, North Carolina, was closed after routine testing found the bacteria in a self-standing cooling tower.

About 400 of the 850 employees who work in Zebulon were told to stay away until the towers were cleaned, the London-based company said.

The company said that the cooling tower "does not come into contact with product manufactured at the facility".

Glaxo did not respond to questions about whether there was any risk of indoor exposure to employees or medicines from water droplets that could carry the bacteria.

"We are trying to gather information on what the situation is," spokeswoman Jenni Brewer Ligday said.

"It was found during routing testing, so we're trying to get a better handle of how often those testings are conducted. Also more details on whether product has been impacted and, if they have, what is our procedure in place to handle that."

The plant produces inhaled drugs like Advair, a drug for asthma, and contracts with other pharmaceutical companies to produce their drugs.

America's Food and Drug Administration is checking reports of the bacteria's discovery. A spokesman had no immediate comment.

State and county health chiefs said they were not aware of any cases of Legionnaires' disease - a potentially fatal form of pneumonia - associated with the Glaxo plant, adding that most people exposed to the bacteria do not become ill.

The same bacteria found in cooling tanks in the Bronx borough of New York City has caused 12 Legionnaires' disease deaths this summer. The Centres for Disease Control and Prevention says about 8,000 to 18,000 Americans are treated in hospital for the illness every year.

People can contract Legionnaires' disease when they inhale water vapour or mist containing the bacteria, the CDC said. It does not spread from person to person.