NEW DELHI — The streets were packed Wednesday night when the first explosion ripped through the air.

A car powered by compressed natural gas was traveling through a bazaar in Dhaka, Bangladesh’s capital, when the cylinder stored in the back exploded, witnesses said.

The blast flipped the car. It then ignited several other cylinders that were being used at a street-side restaurant. Then a plastics store on the ground floor of a nearby building caught fire. Then a small shop that was illegally storing chemicals burst into flames.

A wall of fire surged across the street, engulfing bicycles, rickshaws, cars, people, everything in its path. The inferno claimed at least 70 lives in one of the most historic neighborhoods in Bangladesh, a country where hundreds have died in recent years in fires that tore through crowded, unsafe structures, and where a promised crackdown on building violations has fallen short.