MAYFIELD, United States: US emergency workers searched on Monday for survivors of ferocious tornadoes that killed dozens of people across several states and left towns in ruins, as the governor of hard-hit Kentucky warned that cadaver dogs were still finding bodies. President Joe Biden called the rare late-season burst of twisters in the US heartland "one of the largest" storm outbreaks in American history, and on Sunday night declared a major federal disaster in Kentucky.