WASHINGTON—General Motors Co. said on Thursday it will extend a shutdown of a Michigan assembly plant to mid-October following a new recall of its Chevrolet Bolt electric vehicles over battery issues after 12 reported fires. The largest U.S. automaker said the extension of the production halt at its Orion Assembly plant will go through at least Oct. 15. GM also said it was cutting production at six other North American assembly plants because of the ongoing semiconductor chips shortage. GM said it will not resume Bolt production or sales until it is satisfied that the recall remedy will address the fire risk issue. It said Thursday it had reports of 12 fires and three injuries. GM shares were largely unchanged in late trading. GM in August widened its recall of the Bolt to more than 140,000 vehicles to replace battery modules, at a cost now estimated at $1.8 billion. The …