Lagos, Sep 18 : A four-story building under construction in Nigeria's southern state of Akwa Ibom collapsed, leaving an unknown number of people trapped, a local official said. Located in the Plaza area of Uyo, the state capital, the building fell on another building next to it on Saturday evening, said Godwin Tepikor, coordinator of the National Emergency Management Agency (NEMA) in the southern region, told Xinhua by phone. A combined team of responders from the NEMA and other agencies have arrived at the site to search for people trapped under the debris, Xinhua news agency reported quoting Tepikor. The coordinator said the site has been cordoned off, and the number of casualties is not clear. Since the beginning of the year, at least seven cases of building collapse have been reported, with a death toll of 25. Local experts blame them on aging structures, non-compliance with building planning and regulations, and the use of substandard materials during construction. /IANS