GENEVA (Reuters) - The risk to public health from Japan's nuclear accident is no worse after a change in the disaster's status on Tuesday, the World Health Organization said.

"Our public health assessment is the same today as it was yesterday," WHO spokesman Gergory Hartl told Reuters. "At the moment there is very little public health risk outside the 30-kilometre (evacuation) zone."

The higher severity rating was the result of combining the amounts of radiation leaking from three reactors and counting them as a single incident, he said.

(Reporting by Stephanie Nebehay and Andrew Callus; Editing by Angus MacSwan)