Firefighters had to knock holes in the walls to rescue children

Prosecutors in Mexico have arrested seven regional officials over the deaths of 47 children in a fire at a day-care centre earlier this month.

The attorney general of northern Sonora state said the officials, from the state's finance department, were being charged with negligent homicide.

The department was in charge of the operations at a warehouse next to the nursery, where the fire started.

Investigators found no fire alarms or extinguishers in the warehouse.

The property was used to store cars, tyres and paperwork for the state.

Sonora State Attorney General Abel Murrieta said arrest warrants had been issued for six other Finance Department officials.

"They are employees and officials with the Finance Department who have a direct responsibility for the warehouse where the fire started," he told a news conference.

Investigators said the fire may have been caused by a short circuit or overheating in the warehouse air conditioning system.

The blaze spread to the roof of the day care centre and fire fighters had to knock holes in the walls of the building to rescue children.

Thirty children died on the day of the 5 June fire in Hermosillo and many more were badly injured.

The 47th victim, a three-year-old girl with burns on 65% of her body, died on Sunday.