Mexico drug lord Joaquin Guzman used tunnel for prison break
Mexican drug lord Joaquin Guzman, known as El Chapo or "Shorty", used an elaborate tunnel to break out of a maximum security prison, officials say.
His escape route from Altiplano jail was more than 1.5km (1 mile) long and had ventilation and stairs, the national security commissioner said.
Eighteen guards are being questioned.
Guzman was last seen in the showers of the jail on Saturday. It was the second time he had escaped from a top security prison.
In 2001 he broke out by hiding in a laundry basket after bribing prison officials.
He had been serving a sentence of more than 20 years after being arrested in Guatemala in 1993.
His recapture in 2014 was hailed as a victory for Mexico's government.
Officials say that Guzman's escape was discovered when officers checked his cell in the jail, which is near the capital, Mexico City.
They found a hole around 10m (32ft) deep with a ladder, which led to the tunnel. It came to an end at a construction site outside the prison walls, security commissioner Monte Alejandro Rubido said at a news conference.
A motorcycle was also discovered, which police believe was used to transport tools and remove earth from the space.
A manhunt has been launched and flights suspended at a nearby Toluca airport.
Guzman's wealth is estimated at $1bn (£630m).
His rise to head of the Sinaloa cartel made him the world's most wanted drug trafficker. It smuggles huge amounts of cocaine, marijuana and methamphetamine into the United States.
Before his recapture in 2014, the US state department had offered a reward of up to $5m (£3.2m) for information leading to his arrest.