Mexico will punish those responsible for an overpass collapse that killed at least 24 people and injured dozens when a train on Mexico City's newest metro line plunged onto a busy road below, the government said on Tuesday.

Accompanied by officials involved in the construction and maintenance of the elevated metro line that collapsed on Monday night, President Andres Manuel Lopez Obrador said the investigation should be done quickly and that nothing should be hidden from the public.

"There's no impunity for anyone," he told a news conference. The city has been governed since the turn of the century by former mayor Lopez Obrador and his allies.

The crash has raised wider questions about safety on one of the world's busiest metro systems, which carries millions of people daily across the capital's urban sprawl.