At least six people have died and more than a dozen others injured after tornadoes struck Michigan and Oklahoma, in severe storms that swept across parts of the US. Officials said four people were killed in southern Michigan, including a 12-year-old boy, and two died in Oklahoma on Friday, with rescue workers continuing to assess the damage. The storms uprooted trees, downed power lines, damaged buildings and ripped the roofs off some houses on Friday. The National Weather Service (NWS) said the severe weather could continue into the weekend, warning of thunderstorms and flash flooding from the Great Plains to Texas. In Michigan, the Branch County sheriff's department said three people were killed and 12 others were injured near Union City after a tornado hit on Friday. Power outages and road closures are expected this weekend, they added. About 50 miles (80 km) away in Cass County, Michigan, authorities reported one one death and several injuries.…