Mexico blast hunt for survivors at 'dangerous' phase

Rescue work after a deadly explosion at the headquarters of the Mexican oil company Pemex entered its final and most dangerous phase, the attorney general has said.

Jesus Murillo Karam said there was risk of structure collapse in the last two of the 39 sectors of the affected area.

Authorities say no hypothesis for the blast that on Thursday killed 33 people and injured 121 has been ruled out.

Meanwhile, President Enrique Pena Nieto declared three days of mourning.

Will Grant reports.