Anigerian Air Force plane crashed on Monday in the country's southwest, killing all 32 people on board, President Bola Tinubu said, declaring three days of national mourning.

It is one the worst air disasters in recent years in Africa's most populous country.

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 (0800 GMT), the president and the air force said.

"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," he said.

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 presidency said.

The plane crashed near a naval base, according to the presidency and the 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".

Noise like thunder

Dayo Akinte, 39, a firewood hawker who lives about a kilometre from where the accident occurred, described to AFP hearing a sound she thought was "thunder" at the time she believed the plane went down.

Since the crash, "three aircraft have also been flying over the scene", she said by phone.

She said someone who went fishing in the swamp alerted the nearby naval base and people in the town about the crash.

Airforce spokesman Ehimen Ejodame earlier said "search and rescue operations" were ongoing "in coordination with relevant authorities and emergency response agencies".

Police also confirmed the accident but provided no details.

Igbokoda is located in Ilaje, an oil-producing region in southern Nigeria.

In May 2021, Nigeria's top-ranking army commander, Lieutenant General Ibrahim Attahiru, and 10 other officers were killed when their plane crashed in bad weather while trying to land at northern Kaduna state airport.

Seven people died when a military plane crashed into a house in northern Nigeria killing everyone on board in August 2015.

Earlier that same month, a helicopter crashed into a lagoon in Lagos, killing six, including the American pilot.

Sun News/ rabbi