Police said the bomb had targeted the Marco Fidel Suarez Military Aviation School.

"There was a thunderous sound of something exploding near the air base," 65-year-old eyewitness Hector Fabio Bolanos told AFP.

"There were so many injured people," he said. "Many houses were damaged in front of the base."

Several buildings and a school were evacuated.

Cali mayor Alejandro Eder said preliminary reports indicated at least five people were killed and 36 people were injured.

He announced a ban on large trucks entering the city, fearing further explosions.

Eyewitness Alexis Atizabal, 40, indicated that civilians may be among the dead.

"There were fatalities among people passing by on the avenue," he said.

It was not immediately clear who was responsible, but regional governor Dilian Francisca Toro called it a "terrorist attack."

"Terrorism will not defeat us," she said.

In June, leftist guerrillas claimed responsibility for a wave of bomb and gun attacks in and around Cali that killed seven people.

The group, the Central General Staff (EMC), rejected a 2016 peace deal and has upped operations ahead of elections in 2026.