The toll rose after four victims lost their lives in a hospital, said the Missouri Department of Public Safety in a statement.
Aid to the disaster struck region is being sent by the state Cornish charity ShelterBox. A charity team based in Helston will work with the American authorities and take the boxes to the region containing blankets,cooking utensils and water purification equipments.
"In rural northwest Arkansas, where folks are spread out, it's easy to overlook pockets of the population that are in need of help," said Yi Shun Lai, a member of ShelterBox.
"We've seen folks whose homes are reduced to rubble but who remain on their land for fear of losing even more," he said.
The tornado has been ranked as the seventh most deadliest tornado in the history of US, according to the National Oceanic and Atmospheric Administration (NOAA).