Santiago: Chile's President Sebastian Pinera has declared a state of emergency in the capital Santiago as the city of six million descended into chaos amid riots that left a downtown building engulfed in flames and its metro system shuttered.

A woman shouts protests near the Santa Lucia subway station in Santiago during a protest against the rising cost of public transport fares. Credit:AP

Black-hooded protesters enraged by recent fare hikes on public transportation lit fires at several metro stations, looted shops, burned a public bus and swung metal pipes at train station turnstiles during Friday's afternoon commute, according to witnesses, social media and television footage.

Pinera spoke to the nation in the early hours of Saturday, declaring an emergency lockdown as sirens filled the night air, and police and firefighters rushed to contain the damage.

The centre-right Pinera said he would invoke a special state security law to prosecute the "criminals" responsible for the city-wide damage, while at the same time saying he sympathised with those impacted by the rate hikes.