Flags are waving in the warm evening light in the Zócalo, Mexico City's main square, and thousands of people have gathered to hear Andrés Manuel López Obrador, leader of the country's left, speak out against the government's imminent energy reform proposals.

"If we allow private companies to come in, we would be left without any possibility of developing Mexico," he proclaims, to cheers from the crowd and a sea of fists held high. "How long would it be before we stop being a nation and turn into a colony?"