Colombia will cull some of the 166 hippos descended from a small herd imported by deceased drug lord Pablo Escobar in the 1980s, the country's environment minister said Thursday.

Authorities have tried various approaches to curb the population explosion along the Magdalena River, including sterilization and transferring individuals to zoos abroad.

But they have so far been unable to contain the growth in hippo numbers in Colombia's Antioquia department, thousands of kilometers away from their homeland in Africa.

After cocaine baron Escobar was killed in a 1993 shootout with police, the animals he had imported for a private zoo were left to roam freely in a hot savanna region of Antioquia criss-crossed by rivers, marshes and swamps with abundant hippo food.

Colombia's environment ministry declared the hippos an invasive species last year, opening the door to a cull.

Experts warn the mammals' uncontrolled reproduction poses a threat to the local human population and to wildlife.

Hippos are among the most dangerous animals in the world.

Fishing communities along the Magdalena River have come under attack and some hippos invaded a school yard, though no-one has died in such confrontations.

On Thursday, minister Susana Muhamad told reporters officials will sterilize 20 of the hippos this year, while "some" of the animals would be euthanized, though she did not say how many.

University experts have warned Colombia's invasive hippo population could reach 1,000 by 2035 if nothing is done, but animal activists say sterilization entails suffering for the animals -- and great danger for the vets doing it.