HERMOSILLO (Mexico) - A STATE prosecutor said on Monday that a short circuit or overheating of a cooling system in an adjacent warehouse set off a blaze that killed 44 mainly small children in a Mexican daycare centre.

Abel Murrieta, prosecutor of the northern state of Sonora, raised the death toll from Friday's fire to 44 after another death in hospital, without specifying if the latest fatality was a child or a care worker. Most of the victims of the blaze in the state capital Hermosillo were children under the age of two, and most died from smoke inhalation, officials said.

As anger about the tragedy mounted across Mexico and distraught parents waited for news at hospital burn units, questions were raised about safety conditions at the ABC daycare centre and whether the disaster could have been prevented.

'The fire was generated by the overheating or a short circuit in a machine of a cooling system in the adjacent warehouse,' used for storage by the finance ministry, Mr Murrieta told a news conference, adding that investigators needed to focus on why it had spread so rapidly.

Care workers only noticed the blaze when thin walls between the buildings collapsed and clouds of toxic smoke swept in, Mr Murrieta said. Many of some 141 children in the facility at the time of the fire were taking an afternoon nap.

'Almost the whole roof fell in suddenly, without warning,' said Sonora State governor Eduardo Bours earlier on Monday. News reports said the centre had only one emergency exit which was closed on the day of the fire, and five small windows near the ceiling.

Mr Bours said that three of the centre's owners worked for the Sonora government, including one who was married to a woman related to the first lady, Margarita Zavala. A third belonged to the leftist PRI opposition party which governs the state, Mr Bours said.

Mexican President Felipe Calderon on Sunday called the events 'a painful tragedy for all Mexicans.' Some of the injured were transferred to the western state of Jalisco to be treated by doctors specialised in children's burns, and three were flown to a burns unit at a hospital in Sacramento in the US state of California.

Around 3,000 people had gathered in an auditorium in Hermosillo Sunday to pray for the children who perished in the blaze.

'My niece died but she didn't burn to death, she suffocated. They found her sitting, crouched in a corner,' the relative of one of the victims buried on Sunday told AFP. -- AFP