Six people have died - including three firefighters - after a truck carrying 60 tons of liquefied natural gas crashed and exploded in the Mongolian capital.
Hundreds of firefighters had been sent to battle the blaze following the collision with a car in Ulaanbaatar on Wednesday morning, officials said.
At least 11 people were injured, with the fire spreading to nearby buildings.
One local resident described how he initially thought a plane had crashed.
Erdenebold Sukhbaatar, a 40-year-old lawyer, told Reuters news agency the crash, which took place just after 01:00 local time (17:00 GMT on Tuesday), had felt like an earthquake, but was followed by a bright light.
"It was very strong. And then I've never seen such kind of, like, strong [explosion]. It was like 60, you know, tons, which means 60,000, litres [of gas] you know. It was like huge liquid gas."
He watched the ensuing fire spread to "almost three different buildings", climbing at speed.
One resident told Reuters that by the time they realised their building was alight, their front door had already been engulfed in flames, forcing them to break out of the back door. When they looked back, the fire had reached the top floor of the building.
"It all happened very quickly," they said.
Another described how the force of the explosion had not only blown out their windows, but also destroyed their balcony.
According to Sainbuyan Amarsaikhan, Mongolia's deputy prime minister, no casualties had been reported from inside any of the buildings.
However, he revealed the firefighters died in a second explosion, which threw part of the truck "with a lot of force", resulting in the "tragic loss" of life.
The Mongolian National Emergency Management Agency (NEMA) - which said the fire was put out by 04:30 - added that four children were among the injured, including one who was being treated for poisoning.
Questions are now being asked about why a tank carrying such a dangerous load had been allowed to travel into the residential neighbourhood, containing many schools.
"You know, if it happened [in] the daylight time, especially during the rush hours in the morning or in the evening, [it would] be more harmful," Erdenebold Sukhbaatar pointed out.
"This shows city planning is really bad," Ankhbayar Galbadrakh told AFP news agency. "All of these trucks - with gas or without gas - should travel outside of the city limit."