High aspect ratio Na0.44MnO2 nanowires with a complex one-dimensional (1-D) tunnel structure have been synthesized. We found that the reaction went through layered birnessite nanosheet intermediates, and that their conversion to the final product involved splitting of the nanosheets into nanowires. Based on our observations, a stress-induced splitting mechanism for conversion of birnessite nanosheets to Na0.44MnO2 nanowires is proposed. The final and intermediate phases show topotaxy with 〈001〉f // 〈020〉b or 〈110〉b where f represents the final Na0.44MnO2 phase and b the intermediate birnessite phase. As a result of their high surface areas, the nanowires are efficient catalysts for the oxidation of pinacyanol chloride dye.