A tornado that spun across the Oklahoma-Missouri border killed at least 18 people as severe storms raked the central part of the country Saturday, injuring many and mangling buildings in the storm-weary region. At least 12 people were killed after severe storms spawned tornadoes and high winds across sections of southwestern Missouri, the State Emergency Management Agency said. Ten of the dead were killed when a twister struck near Seneca, near the Oklahoma border. At least six people were killed as the tornado flattened the northeastern Oklahoma town of Picher, authorities said. "They're going over the hard-hit area and turning over everything and looking," SEMA spokeswoman Susie Stonner said of emergency workers' search for victims and assessment of damage. "It's hard to do in the dark."