Story highlights The blaze started after some residents set fire to a mattress, Guatemalan official says

Guatemalan President Jimmy Morales declares three days of mourning

(CNN) Forty people -- mostly teenage girls -- were killed after a fire tore through a youth home in San Jose Pinula, Guatemala.

Wednesday's blaze started when some of the youths at the Virgen de la Asunción Safe Home set fire to a mattress on their way to breakfast, said Abner David Paredes Cruz, an attorney with the office of Guatemala's human rights prosecutor.

Nineteen female residents of the home near Guatemala City -- all between 13 and 17 -- died at the scene, the country's National Civil Police told CNN en Español.

Video from the scene showed sobbing family members outside the home, banging on doors and looking for loved ones.

Twenty-one others died at hospitals in Guatemala City, according to information released by the Guatemalan Ministry of Health and the hospitals. The fire, which began around 9 a.m. (10 a.m. ET) Wednesday, left many others injured.

Guatemalan Red Cross members arrive at the Virgen de la Asunción Safe Home in San Jose Pinula.

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