The incident occurred at about 0645 GMT shortly after the MI-35P helicopter took off for an operation in the oil-rich Rivers State, a region rife with rampant oil theft, Air Force spokesperson Edward Gabkwet said in a statement.

The crew members are being treated at an Air Force medical centre in Port Harcourt, he said.

(Writing by Elisha Bala-Gbogbo; Editing by Gareth Jones)