Mexico's government has offered a US$3.8 million reward for the capture of fugitive drug lord Joaquin "El Chapo" Guzman and sacked top prison officials amid suspicions guards helped him escape.
Guzman vanished from his cell late on Saturday even though he was wearing a monitoring bracelet and surveillance cameras were trained on the room 24 hours a day, Interior Minister Miguel Angel Osorio Chong said.
Osorio Chong said Guzman "must have counted on the complicity of prison personnel... which if confirmed would constitute an act of treason".
Guzman had been behind bars for just 17 months when he escaped for the second time since 2001, dealing a humiliating setback to President Enrique Pena Nieto and overshadowing a state visit to France.
This time, the head of the Sinaloa drug cartel managed to flee a maximum-security prison 90 kilometres west of Mexico City through a 1.5-kilometre tunnel found under his cell's shower.
"What happened two days ago is a terrible event that has angered Mexican society," Osorio Chong said on Monday.
While cameras were constantly trained on the cell, Osorio Chong said there were "two blind spots" to respect the inmate's privacy "and human rights", and he managed to remove the bracelet, which only worked inside the prison.
Osorio Chong said he decided to fire the Altiplano prison's director as well as the head of the nation's penitentiary system and general co-ordinator "to facilitate" the investigation.
Attorney-General Arely Gomez said 34 prison officials and 17 inmates were interrogated by prosecutors. No charges have been announced so far.
A federal official said prison employees of various rank, including the warden, spent the night at the anti-organised crime unit of the attorney-general's office.
Two of Guzman's lawyers were questioned and anyone who visited him during his incarceration is being sought.
The owner of the property where Guzman's tunnel ended also faced questioning.
The Government has launched a massive manhunt for Guzman, who amassed a huge wealth as the head of the country's most powerful drug gang, with tentacles reaching around the globe.
Troops and police patrolled highways, borders and airports, while the governments of the US and Central American neighbours were co-operating.
The US State Department said Guzman's "swift recapture by Mexican authorities is a priority for both the Mexican and the US governments".
Osorio Chong urged Mexicans to help authorities find Guzman. The reward offered by the Government, 60 million pesos, is double what it usually gives for top drug lords.
"There will be no rest for this criminal," he said. "There will be no break in efforts to rearrest him."
The Government released a recent photo of Guzman, with his head and famous black moustache shaved off.
Osorio Chong said Mexicans should be safe calling an anonymous tips hotline.
Mike Vigil, a retired US Drug Enforcement Administration international operations chief, warned that if Guzman is not captured in the next day or so, he will vanish for good.
"If he is able to make his way to Sinaloa, his native state, and gets into that mountainous range, it's going to be very difficult to capture him because he enjoys the protection of local villagers," Vigil said in an interview.