A polio-like illness has afflicted a small number of children in California since 2012, causing severe weakness or rapid paralysis in one or more limbs.

The Los Angeles Times reported that state public health officials had been investigating the illness since a doctor requested polio testing for a child with severe paralysis in 2012. Since then, similar cases have sporadically been reported throughout the state.

Dr Carol Glaser, leader of a California department of public health team investigating the illnesses, said she was concerned about the request because polio had been eradicated in the US and the child had not travelled overseas.

The symptoms sometimes occur after a mild respiratory illness. Glaser said a virus that is usually associated with respiratory illness but which has also been linked to polio-like illnesses had been detected in two of the patients.

Dr Keith Van Haren, a paediatric neurologist at Stanford University's Lucile Packard children's hospital who has worked with Glaser's team, will present the cases of five of the children at the American Academy of Neurology's upcoming annual meeting.

He said all five had paralysis in one or more arms or legs that had reached its full severity within two days. None had recovered limb function after six months.

"We know definitively that it isn't polio," Van Haren added, noting that all the children had been vaccinated against that disease.

Glaser would not say how many cases were being investigated. Van Haren said he was aware of about 20.

She urged doctors to report new cases of acute paralysis so investigators could try to determine the cause.