As many as 20 kids have been affected by a mysterious polio-like syndrome in California since 2012, leaving them with paralysed limbs.

The state public health officials and physicians have been investigating the illness since a doctor recommended a polio testing for a child with severe paralysis in 2012, reports The Los Angeles Times.

Dr Carol Glaser, leader of a California Department of Public Health team investigating the illnesses said that a virus may be behind the disease, which is occurring sporadically throughout the state.

Symptoms have ranged from restricted movement in one limb to severe weakness in both legs and arms, and sometimes a mild respiratory illness.

Glaser said two of the affected kids tested positive for enterovirus-68, a virus that is usually associated with respiratory illness but which has been linked to polio-like illnesses as well.

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 in Philadelphia.

He said all five patients had paralysis in one or more arms or legs that 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 had been vaccinated against that disease.

While the infection remains rare, doctors say they do not expect an epidemic of the polio-like virus.

Polio is a highly infectious disease caused by a virus, mainly affecting children under the age of five. It invades the nervous system and can cause total paralysis in a matter of hours.