In northern Nigeria's Yobe state, a suicide bomber has killed several people at a venue televising a World Cup match, residents and medics say. A hospital worker told that truckloads of injured people are being treated in overcrowded wards. The injured people are so numerous they cannot be counted, the worker said after the blast hit Damaturu town. An emergency has been declared in three states, including Yobe, amid attacks by suspected Boko Haram militants. Witnesses say the suicide bomber in a tricycle taxi detonated the explosives as people watched Brazil's match against Mexico yesterday evening.