Updated

Authorities in this southwest Missouri city hammered by a tornado that killed at least 122 people believe that many, if not most, of those considered "unaccounted for" survived the storm safely.

Still, they sent rescue teams back out Wednesday to comb through the debris for a fourth time in a search for survivors of the nation's deadliest single tornado since 1950.

Authorities said it is impossible to know exactly how many people are missing and have cautioned the fact that people are unaccounted for does not necessarily mean they are still trapped in debris or have died.

"There has been information in news sources that 1,500 people are missing," City Manager Mark Rohr said. "That does not mean they are injured or deceased. It means that loved ones are not aware of their whereabouts. We understand that some people may have been out of the area when the storm hit or have since left."

Rohr and Fire Chief Mitch Randles declined to speculate on whether the death toll from Sunday's storm will grow substantially. It wasn't clear Wednesday when the search operation would switch from rescue to recovery.

Randles said rescuers are confident that no additional bodies will be found at one of the hardest hit areas in Joplin, a Home Depot store that was flattened by the tornado.

Bob Benson, a Red Cross official who set up a "Safe and Well" registry at a shelter on the Missouri Southern State University campus, said a small number of parents have arrived looking for lost children. More than 100 people have come to him seeking information on missing senior citizens.