Beijing's Communist Party chief Cai Qi visited both the injured in hospital and the fire scene, the official Xinhua news agency said, adding that police had detained the building's owner.
The visit by Cai -- a rising political star -- underscored government concern about the unfolding public relations disaster that has followed the city's brutal response to last month's dormitory fire.
City officials began tearing down unsafe buildings in late November after a fire that killed 19, driving residents out into the winter cold with little notice in the name of fire safety, a move that has provoked public outroar.
Wednesday's blaze started at around 1:18 am when two electric bicycles caught fire, Xinhua said, citing the fire department. The house was "self-built for rental", Xinhua reported.
Seventy shops, 3 houses gutted in Chitral market fire
The vehicles are a popular means of transportation for the many migrant workers who have flooded into the capital city from around the country in search of work.
Dozens of police and onlookers gathered behind yellow tape sealing off the scene, watching fire inspectors and local government officials go about their work.
The neighbourhood is a collection of crude homes that have sprung up across the street from a massive wholesale market specialising in home fixtures, such as doors and lamps, an area well-known to the city's many itinerant construction workers.
In recent weeks, authorities have torn most of the buildings to the ground. Furniture, clothes and even food littered the piles of rubble surrounding the fire scene, evidence that former residents were driven out by authorities without time to collect their belongings.
Fire safety is a major problem in the city's cheap migrant housing, which often features jerry-rigged electrical wiring and no easy way to flee a blaze. But the brutal efficiency of the demolitions and mass evictions has provoked an unusual public outcry that has put officials on edge.
COMMENTS
Comments are moderated and generally will be posted if they are on-topic and not abusive.
For more information, please see our Comments FAQ