Those injured in the blasts at the factory in Tamil Nadu state's Virudhunagar district were taken to a nearby hospital for treatment, police officer Raj Narayanan said.
The building is flanked by a school and a nursing home in Spain's capital. Residents from the latter were being evacuated shortly after the blast, according to eyewitnesses.
Kosovo police say that more than 40 people were injured on Tuesday in a suspected gas tank explosion in the town of Ferizaj.
A chemical leak was thought to be the reason the blaze kept burning despite firefighters best efforts.
Wednesday's 6 1/2-minute test flight was the most ambitious to date. It didn't end as planned, however.
Police are investigating the blasts and have not revealed a possible motive.
A risk assessment of the underground depot carried out over the previous two years said it presents "unacceptable" risks based on current safety regulations.
The explosion was detonated at an old power plant in Alabama.
One of the trains was loaded with dangerous materials, including flammable gas and a corrosive substance.
Both Lebanese protesters and members of the international community have called for an impartial investigation into the incident that killed more than 170 people and injured thousands.
Lebanon's Health Minister warned 'there are probably more (victims) under the rubble".