In the U.S state of Missouri, bad weather is hampering rescue efforts as crews claw through rubble searching for survivors of the deadly tornado. President Barack Obama says he is heartbroken over the devastation wrought by the massive storm that killed 116 people in the town of Joplin over the weekend. He will visit the disaster zone on Sunday, following his four-nation visit to Europe. Shocked residents in Joplin are digging through the rubble of their homes, astonished by the extent of the devastation. More than 2,000 buildings were damaged or destroyed, when the twister came roaring through with just a 24-minute warning. Meanwhile, Joplin residents have been warned that more potent storms are on the way. More severe weather is also forecast for Oklahoma, Kansas, extreme northern Texas and south-western Missouri.