Lagos, Nigeria - A Nigerian Air Force plan crashed on Monday in the country's southwest, killing all 32 people on board, President Bola Tinubu said, declaring three days of national mourning.

The passenger aircraft was on a "routine mission" from Benin City in southern Nigeria to the economic hub of Lagos when it went down at Igbokoda in southwestern Ondo state shortly after 9:00AM on Monday, the president, and the air force said.

At least 32 people have been killed in the crash, which is one the worst air disasters in recent years in Africa's most populous country.

"The president extends his deepest condolences to the family of the 25 passengers and seven crew members involved," Tinubu's office said in a statement. "This is a painful moment for our armed forces and for the entire nation."

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Tinubu's spokesman Bayo Onanuga said in a later statement that the president "has declared a three-day national mourning for Air Force personnel who died in the crash."

He also directed that flags be flown at half-staff across the country to pay respect to the officers. The Air Force will release the identities of the victims after notifying their families.

The plane crashed near a naval base, according to the presidency and Aviation Minister Festus Keyamo. Both described it as an ATR-42 – a twin-engine turboprop that the manufacturers say can carry between 30 and 50 passengers.

A video circulating on social media showed a small crowd gathered near a river while rescuers searched the area by boat.

The president said he had "directed the Nigerian Air Force to immediately commence a thorough investigation into the cause of the crash to prevent future occurrences."