Nine people are still in critical condition four days after a Beijing building fire killed 18 and injured 24, the municipal health authority said Friday in a statement.

Of the 24 injured, 16 had their tracheas cut open to facilitate breathing while the nine in critical condition were put on breathing machines, the bureau cited health experts as saying.

All the 24 sustained injuries to their respiratory systems while some had burns covering 98 percent of their bodies, according to the statement.

The patients are under the care of doctors at the Beijing Jishuitan Hospital, one of the country's best hospitals in treating burns.

The fire broke out around 1 a.m. Monday in a building in the town of Jiugong in Beijing's southern Daxing District.

An investigation into the fire indicated that a malfunctioning electric tricycle stored in the building was to blame for the accident.

The first floor of the four-story building was used as a garment workshop, from where the fire erupted.

Most of the victims were migrant workers living in the building.

Monday's fire was the most fatal one in Beijing in about nine years. In June 2002, an underground Internet cafe fire claimed 25 lives, mostly college students.