SOUTH SIOUX CITY, Neb. — Authorities have not let northeast Nebraska residents who live near a grain elevator damaged in an explosion return to their homes, fearing the structure could collapse at any moment.

Tuesday’s blast blew a gaping hole into the Andersen Farms elevator in South Sioux City, injuring two people. City Police Chief Ed Mahon told the Sioux City (Iowa) Journal that inspectors haven’t identified the cause of the explosion.

The structural integrity of the 230-foot tower also remains uncertain, Mahon said. Engineers hope to tear down the elevator in a controlled fashion before it falls on its own.

The evacuation zone has been reduced, so some residents living near the grain elevator have gone back to their homes. Residents who are still restricted from their homes were permitted to return briefly to retrieve belongings.