Drug lord Joaquin “El Chapo” Guzman has escaped from a maximum-security prison in Mexico by tunneling out of the facility. The former leader of the Sinaloa cartel had been incarcerated inside the Altiplano prison facility for the past eighteen months. Guzman apparently escaped the prison by sneaking through a passage in the shower area of his cell that connected to a nearly mile-long tunnel running underneath the prison.

The escape set off a massive manhunt for Guzman, the world’s most famous drug lord, in the early hours of Sunday morning. The Altiplano prison was put on lockdown after Guzman’s escape and police were deployed to the surrounding areas to search for the drug lord. The nearby Toluca airport had all flights grounded to prevent Guzman from flying out of the range of the authorities.

According to Mexico’s national security commissioner, Monte Alejandro Rubido, Guzman was last seen inside the prison around 8 p.m. while being given medication. The discovery of the tunnel indicates that Guzman’s escape was well planned and probably financed by cartel members. The tunnel was illuminated, had PVC piping for ventilation, and was equipped with an adapted motorcycle-on-rails to aid the escape. There are also indications that the escape may have occurred with the complicity of officials inside the prison.

Mexican President Enrique Peña Nieto has focused on arresting and incarcerating top drug bosses from all the major cartels during his tenure. The Altiplano federal facility has been called the country’s most impenetrable prison and has held a number of top cartel members over the past few years. However, the failure to hold the country’s most important drug trafficker is a staggering blow for the president’s administration.

This is the second time Guzman has escaped from prison in his drug-running career. He escaped from another Mexican maximum-security prison in 2001. After evading capture for years, Guzman was captured by a team of Mexican commandos in February 2014 while sleeping in a condominium in the beach town of Mazatlan. It is believed that he may be hiding out in the cartel’s hideouts, safe houses and drug ranches in the northern Sierra Madre Mountains.