QUITO, Ecuador — Angry demonstrations over Ecuador’s elimination of fuel subsidies widened on Friday, paralyzing much of the country for the second consecutive day as protesters in the capital clashed with riot police officers who used tear gas and armored cars to disperse them. Hundreds of people were reported arrested.

The mayhem in Ecuador, a country with a history of political convulsions and economic crises, represents the biggest challenge to President Lenín Moreno since he took office in a 2017 election after a decade in power by Rafael Correa, a former ally. The end of Mr. Correa’s tenure was punctuated by accusations of corruption involving public infrastructure projects and a swelling of the country’s foreign debt.

Mr. Moreno decreed a 60-day state of emergency on Thursday, when the fuel subsidies repeal took effect, as strikes and violent protests by transport workers and others made much of Ecuador come to a standstill.

The president, now an adversary of Mr. Correa’s, vowed there would be no turning back on ending the fuel subsidies. “Under no circumstances will we change the measure,” he said.