A shopping plaza under construction in Nigeria's southeastern Anambra state collapsed, killing at least six people, with others feared trapped in the rubble, the emergency agency said. The building, with more than 120 shops, collapsed in the city of Onitsha, the National Emergency Management Agency (NEMA) said on Tuesday. "Some of the rescued persons have been taken to different hospitals in Onitsha for treatment," NEMA said. A search was underway for other survivors, it said. Building collapses are frequent in Africa's biggest economy and top oil producer due to lax regulations and often substandard construction materials.