A sinkhole that appeared in a Puebla field late last month has continued to expand, eating its way into the perimeter wall of a house and forcing authorities to widen a security perimeter around it.

The big hole in Santa María Zacatepec, about 20 kilometers northwest of Puebla city, had grown another 13 meters as of Monday, measuring 110 meters across at its widest point. Its total area is 11,000 square meters.

The nine-meter-deep sinkhole has already destroyed a bedroom and part of a wall of a house that sits on the edge.

Among the possible causes are a geological fault or variations in the soil’s water content, according to scientists and authorities. Some locals believe that it’s related to the overexploitation of groundwater reserves.

One architect has speculated there could be an underground river at the base of the sinkhole after evaluating photos taken by a drone.

Interior Minister Ana Lucía Hill Mayoral said that over the weekend authorities carried out geophysical, hydrological and chemical studies to ascertain the cause, and that conclusions will be drawn in the coming days.

Magdalena Xalamihua, who lived with her husband and two children in the endangered home, said that they noticed a sulfur smell three days before the sinkhole appeared.

Nicasio Torres, 62, who has lived in Zacatepec all his life, echoed the fears of his neighbors. “We worry that it will continue to get bigger,” he said after arriving at the sinkhole on a bicycle. “What is going to happen to us? Are they going to evacuate us? We don’t have anywhere to go,” he added.

The sinkhole measured only 10 meters across when it appeared May 29.

It has become an attraction for Puebla residents and local police have taken action to prevent traffic on ground that has already proven itself to be fragile.

With reports from El País (en), Milenio (sp), El Universal (sp)