Sculptures by Colombia's most famous artist, the world-renowned Fernando Botero, unwittingly found themselves thrust into the midst of an anti-pollution protest Friday when activists strapped surgical masks on their giant faces.

The iconic sculptures are in a downtown plaza in Medellin, Colombia's second most populous city and the 83-year-old Botero's hometown.

"We came to the place that we love the most, Plaza Botero... but which is also the most polluted part of the city of Medellin according to our sensors," said Carlos Cadenas of the Green City collective environmental group.

"We designed masks for all of the sculptures and we installed them," Cadenas told AFP.

Group members are also petitioning the government for "a real solution" to the pollution problem, not just "waiting for the weather to change" so that the wind and rain will clean the air.

Some surprised pedestrians put on surgical masks that the activists handed out.

Officials declared an environmental alert in Medellin in March due to a "considerable increase" in dangerous airborne pollution.

Air quality remains bad enough to harm young children and the elderly, even after a two-day ban on automobiles in early April.

Carmen Zapata, head of the Air Quality Laboratory at Medellin's Universidad Nacional, said that pollution levels are especially high because there has been no rain due to the El Nino weather phenomenon, and due to a change in the wind patterns.

"The rainy season and public awareness are fundamental to lower the pollution indices," Zapata said.

The environmental activists at the plaza were also promoting a forum in October in Medellin aimed at discussing ways to implement in Latin America the agreements reached at the Paris climate talks in late 2015.