Security forces in Mexico are searching for one of the world’s most powerful drug lords, Joaquin “Chapo” Guzman, following his escape from a maximum-security jail on Saturday.
Helicopters were seen circling above the Altiplano prison 90km (55 miles) west of Mexico City. Flights from nearby Toluca airport were suspended.
Guzman fled through a 1.5km-long (1 mile) tunnel after 17 months in jail.
It is the second time Guzman has escaped from a top-security prison.
Master of escape
In 2001 he broke out from Puente Grande jail reportedly hidden in a laundry cart after bribing officials.
He was on the run for 13 years before being re-arrested in February 2014. The capture was seen as a coup for President Enrique Pena Nieto.
Dozens of prison guards are being questioned, including the warden of Altiplano prison, to find out how he could escape this time.
Video footage showed Guzman entering the shower area in his cell at 20:52 local time (01:52 GMT Sunday), National Security Commissioner Monte Alejandro Rubido said.
When he did not emerge, guards searching the cell found a hole in the shower area, and a tunnel leading to an outside building, Mr Rubido added.
The tunnel, which measures 1.7m by 70cm would have allowed Guzman, who is known as El Chapo or Shorty, to comfortably walk upright.
It had ventilation and lights and guards also found a motorbike which they believe was used to transport dirt to the outside.
Inside the building, officials found a bed and a kitchen, suggesting those who dug the tunnel could have spent days at a time there.
Local media quoted neighbours as saying that the building had been “built quickly” within the past year.
One neighbour told reporters that he had heard a helicopter overhead on Saturday night but it was not clear if it was used in Guzman’s getaway or was part of the search launched by security forces.
Guzman’s escape is a serious blow to President Pena Nieto, who called it “an affront to the state”.
Shortly after Guzman’s arrest last year, the president said that another escape would be “unforgiveable”.
The president said he was confident that security forces “have the strength and determination to recapture this criminal”.
US Attorney General Loretta Lynch offered help for his “swift recapture”.
Following his arrest, US prosecutors said they would request Guzman’s extradition to the United States, where he has been indicted on drug trafficking charges.
But after Mexican officials insisted they wanted to try him first, a formal extradition request was not filed.
Mr Rubido said roadblocks had been set up around the jail and the prison perimeter had been strengthened.
Border forces in Mexico’s southern neighbour, Guatemala, have also been put on heightened alert.
It was there that Guzman was captured in 1993.
The authorities are also focusing on his home state of Sinaloa, from where he ran the cartel of the same name.
While the Sinaloa cartel has lost ground to rival cartels in past years it continues to be one of the most powerful drug trafficking organisations in the world.
Guzman’s personal fortune is estimated at $1bn (£640m).