Heavily armed gangs attempted to seize control of Haiti’s main international airport, exchanging gunfire with police and soldiers trying to repel them.

The Toussaint Louverture International Airport was shut down when the attack occurred Monday, with no planes operating and no passengers on site, and it marks the biggest attack on the airport in Haiti’s history.

The attack occurred just hours after authorities ordered a nighttime curfew following an explosion of violence in which armed gang members overran Haiti’s two biggest prisons, freeing thousands of inmates over the weekend.

Haiti’s prime minister is currently overseas trying to salvage support for a U.N.-backed security force.

The United States is urging all Americans in Haiti to depart as soon as possible.