MEXICO CITY (AFP) - Mexico's government offered a US$3.8 million (S$5.2 million) reward for the capture of fugitive drug lord Joaquin "El Chapo" Guzman on Monday and sacked top prison officials amid suspicions that guards helped him escape.

Guzman vanished from his cell late 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's administration.

This time, the head of the Sinaloa drug cartel managed to flee a maximum-security prison west of Mexico City through a 1.5-km tunnel found under his cell's shower.

"What happened two days ago is a terrible event that has angered Mexican society," Osorio Chong said.

While cameras were constantly trained on the cell, Osorio Chong said there were "two blind spots," while the bracelet 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 coordinator "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-organized crime unit of the attorney general's office.

The guards in charge of the capo's cell and those who monitored the surveillance cameras that look into the room were among those interrogated, the official said.

Two of Guzman's lawyers were questioned and anybody else who visited him during his incarceration is being sought.

The owner of the property where Guzman's tunnel ended also faced questioning.

- 'No rest for Guzman' -

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 United States and Central American neighbors were cooperating.

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.

"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 mustache shaved off.

Mike Vigil, a retired US Drug Enforcement Administration (DEA) 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.

- Shower escape -

Guzman was last seen right before 9.00 pm on Saturday, when he went into his private shower. After he failed to come out, guards found a hole 10 metres deep with a ladder inside.

The gap led to a sophisticated tunnel with a ventilation and light system that ended inside a gray brick building on a hill surrounded by pastures in central Mexico State.

A huge water pipeline project is under construction around the prison, which could explain why the tunnel's construction went unnoticed.

Guzman's first escape was in 2001, when he slipped past authorities by hiding in a laundry cart in western Jalisco state. He had been captured in Guatemala in 1993.

Marines recaptured him in February 2014 in a pre-dawn raid at a condo in Mazatlan, a Pacific resort in Sinaloa state, with the DEA's help.

Losing Guzman was an embarrassing blow to Pena Nieto, who has won praise for capturing a slew of kingpins, with Guzman - a diminutive but feared man whose nickname means "Shorty" - the biggest trophy.

Some US prosecutors wanted to ask for his extradition following last year's arrest, but Mexican officials insisted on trying him first.