Troops have been patrolling the streets of the Chilean capital Santiago after President Sebastian Pinera evoked a state of emergency amid a surge in violent protests over a hike in public transport fares, the military has confirmed.

Hundreds of thousands of commuters were trapped on their way home from work in Santiago on Friday after high school students flooded subway stations as part of protests against a fare hike.

The capital city descended into chaos amid riots that left a downtown building engulfed in flames and its metro system shuttered.

Subway services in Santiago were suspended after activists jumped turnstiles, dodged fares and vandalised stations as part of demonstrations which quickly spread throughout the city of six million.