Residents of Alagoas state capital Maceio have been nervously watching chemicals giant Braskem’s ‘Mine 18’ since city officials declared a high alert on Nov 29, warning it risked collapsing and causing a potentially massive tragedy.

“Mine 18 suffered a rupture today” in a sector along the city’s lagoon, Mayor Joao Henrique Caldas wrote on X, formerly Twitter.

“The Maceio emergency response department emphasises the mine and its surroundings are unoccupied, and there is no risk to people. We are gathering further information and will share it as soon as possible.”

Video aired on Brazilian media showed large brown bubbles burbling on the surface of the water at the moment of the rupture in the mine, which sits mostly under the lagoon.

Braskem said in a statement an “atypical movement” had been detected at the mine, and that it “continues collaborating” with authorities.

Rock salt is an ingredient in PVC pipe and lye.

Braskem, which operates 35 mines in Maceio, is majority-owned by Novonor, the company formerly known as Odebrecht, which was caught up in a massive corruption scandal in the 2010s.

Maceio, population one million, has had city life upended by Mine 18 since residents were forced to begin evacuating the area around it in 2019, after cracks started to appear in streets and buildings.

An area of 14,000 buildings that was once home to 55,000 people has now been turned to a ghost town.

The earth has recently been sinking in the area around the mine.

The mayor warned the city faced “the biggest unfolding urban tragedy in the world” if it collapsed.

Ecologists warn a collapse could also cause an environmental disaster for the lagoon and surrounding ecosystem.