Two powerful earthquakes struck near Venezuela’s capital Caracas on Wednesday evening, collapsing buildings and sending residents into the streets. The U.S. Geological Survey warned that high casualties and widespread damage are likely. The back-to-back quakes struck a densely populated region on a national holiday, when more people than usual were at home, raising the risk of casualties.

The first earthquake, of magnitude 7.2, hit at 6:04 p.m. local time, and a second of magnitude 7.5 followed less than a minute later, according to BBC News. The U.S. Geological Survey reported high casualties and widespread damage are likely, estimating a 44% chance that fatalities will exceed 10,000 and a 30% chance that they will exceed 100,000. The USGS said aftershocks may still occur.

The epicenter was about 17 miles northwest of Montalbán, an area that is home to some of the country’s largest oil refineries, according to CNN.

Venezuelan Interior Minister Diosdado Cabello said he has asked people to leave their homes, citing damaged buildings and concerns about gas leaks, according to BBC News. Companies cut gas lines to some areas as a precaution, Cabello said. Venezuela’s Ministry of Communication and Information said security forces have been deployed around the country because of the risk of building collapses.