Thunderstorms pummel US disaster zone SEVERE thunderstorms have barreled through Oklahoma City, upsetting relief and clean-up efforts three days after a powerful tornado killed 24 people and destroyed thousands of homes. The dark threatening skies on Thursday cast a pall over the first of a series of funerals in the coming days for the seven children killed in a primary school that took a direct hit from the twister. Heavy rain was forecast for much of the day, soaking the disaster zone where residents had just the day before, under clear blue skies, picked through the rubble of their shattered houses to recover personal effects. Localised street flooding complicated access for emergency and clean-up vehicles, while construction workers and utility linemen took temporary refuge in their trucks to avoid exposure to lightning strikes. "My biggest concern is not necessarily for the structure, but for people's contents," general contractor Lane Yeager told AFP as he scrambled to patch up the roof of a stricken home. They just survived the tornado. Now they're going to have more problems (with rain damage). If we can get the lightning to let up for a little while, we're going to try to cover that up so they don't have further damage. Monday's exceptionally strong tornado -- one of the worst in recent years in the United States, which gets the majority of the world's twisters -- touched down with little advance notice, cutting a 27 kilometre swath of destruction. The Oklahoma Department of Emergency Management has said 2400 homes were damaged and 10,000 people affected, in a community of 56,000 that was hit by an even deadlier twister in May 1999. On Thursday, Governor Mary Fallin's office updated the number of injured to 377. "All people thought missing have been accounted for at this time," it said. Initial damage estimates are running as high as $US2 billion ($A2.07 billion). In an Oklahoma City funeral home, some 250 family and friends gathered on Thursday to mourn the loss of Antonia Candelaria, age nine, one of the seven children who died in the rubble of Plaza Towers Elementary School. Like most schools in tornado-prone Oklahoma, the school had no purpose-built storm shelter for its nearly 500 students and staff. In an online obituary, Antonia's family remembered "Tonie" as a "beautiful young lady inside and out" who had auditioned to sing for her classmates on the last day of school, which would have been Thursday. "We will miss our precious little 'Ladybug' every day, but will rejoice for the day we will be reunited with her again someday," the family wrote. President Barack Obama is scheduled to meet survivors on Sunday and inspect the awesome scale of the destruction in a tight-knit community that suffered an even deadlier tornado in May 1999 that followed roughly the same track. On the Enhanced Fujita scale, that measures a tornado's strength based on the damage it causes, the twister was an EF-5, the highest possible level, said Kelly Pirtle of the National Weather Service's Severe Storms Laboratory. While the United States gets 75 per cent of all the world's tornadoes, very few of them are greater than an EF-2, said John Snow, a meteorology professor and tornado expert at the University of Oklahoma. The epic twister flattened block after block of homes, hurling cars through the air, downing power lines and setting off localised fires in a 45-minute rampage. Moore Mayor Glenn Lewis said he would propose an ordinance to require storm shelters in all new homes. Few homes now have underground safe rooms, due to their high cost and the difficult nature of Oklahoma's flat clay terrain.