(Reuters) - A possible cluster of cases of acute flaccid myelitis, a rare condition that causes weakness or paralysis in children, is being investigated in King County, Washington, the state health department said on Tuesday.

King County, the state's largest county, encompasses Seattle.

An additional possible case of AFM, which affects the central nervous system, brings the total number of confirmed or suspected cases to nine, a spokeswoman for the Washington State Department of Health said in a statement.

Two of the nine have been confirmed as suffering from AFM, the department said, with seven still being evaluated. One child has died, although it was not clear if he or she had the condition.

According to the U.S. Centers for Disease Control and Prevention website, cases of the rare disorder have been on the rise this year, with 89 confirmed cases in 33 states as of September.

Last year, there were only 21 cases of the disorder, a mild year that followed a major outbreak in 2014, when 120 people were reported to have developed the polio-like nerve condition from August to December.

AFM is characterized by a sudden onset of limb weakness and loss of muscle tone and reflexes. Some patients also suffer facial droop or difficulty moving the eyes or swallowing.

It is believed to stem from a variety of causes, including viral infections.

(Reporting by Dan Whitcomb; Editing by Leslie Adler)