A group of 132 inmates escaped from a Mexican prison near the US border, fleeing through a tunnel dug in an old carpentry workshop, the state prosecutor's office said.
The escape sparked a massive manhunt, with federal police and the Mexican army deployed on roads and highways near the correctional facility in Piedras Negras, a city bordering the Texas town of Eagle Pass.
The US Border Patrol was also taking part in the search, Coahuila state attorney general Homero Ramos Gloria told Milenio television.
The prison's director, security chief and shift guard were questioned over the escape and authorities have asked a judge to issue a detention order against the three, the state attorney general's office said in a statement.
Ramos Gloria told reporters that the escape took place at 2:15 pm local time but that it took about an hour for prison guards to notice it, according to the newspaper El Universal.
The tunnel used by the prisoners was 2.90 meters (9.5 feet) deep, 1.20 meters wide and seven meters long, and its exit hole was at the prison's northern tower, the statement said.
After emerging from the tunnel, the inmates "cut a wire fence from where, according to prison authorities, the convicts got out one by one and reached a vacant lot," it said.
The evidence gathered by prosecutors includes fragments of a BlackBerry phone, pieces of a SIM card, a pair of flip-flops, two other flip-flops, three 1.20-meter-long pieces of rope, an electric wire and a broken padlock.
The prosecutor's office said 86 of the inmates were in prison for federal crimes while the other 46 faced different charges.
The state government offered rewards of 200,000 pesos ($15,600) for information leading to the capture of each inmate.
Authorities in Coahuila said that a special police unit killed four suspects in a clash in the town of Castanos four hours after the Piedras Negras escape was reported, and that there are indications that the dead were inmates.
Several mass prison breaks have taken place in Mexico since 2010.
The biggest to date was on December 17, 2010, when 141 inmates escaped from the Nuevo Laredo prison in the northeastern state of Tamaulipas.
Last February, 30 members of the Zetas drug gang escaped from a prison in the northern state of Nuevo Leon during a prison massacre that left 44 inmates from the rival Gulf cartel dead.
Some prison guards confessed to taking part in the plot.
Mexico's prisons are often the scene of riots and murders, which left 171 people dead in 2011, according to the National Human Rights Commission.
The Piedras Negras prison, with a capacity for 1,000 prisoners, was housing 734 inmates when the escape took place, Ramos Gloria was quoted as saying.