A huge fire at a Madrid power substation triggered explosions and led authorities to shut down the centre of the city, jangling nerves four months after train bombings killed 191 people.
Billowing smoke thick enough to block out the sun rose over the Paseo del Prado, Madrid's main thoroughfare. Eleven people were treated for smoke inhalation, an official said.
Police and fire-fighters cordoned off streets, and the clamour of sirens returned to the neighbourhood around the Atocha station where two of four commuter trains were attacked by suspected Islamic militants on March 11.
"My first reaction was fear, because you don't know what it is," said Montse Sanchez, a 34-year old administrator whose journey home was interrupted by the fire.
"I thought 'Oh my god, we cannot cope with another thing like the March 11 bombs'."
The doors of the city's showpiece Prado museum were closed to visitors as an acrid chemical smell permeated the area and several buildings were evacuated.
Police said the cause of the fire was unknown.
The blaze at the substation, which belongs to Spanish utility Union Fenosa, had been largely brought under control by mid-afternoon, some two hours after it began, said a spokesman for Madrid's fire-fighters.
However some 8,000 people remained without electricity, Esperanza Aguirre, head of the Madrid regional government, told state radio. "There are 11 people suffering from smoke inhalation," she added.
A brief power cut affected floor trade at the Spanish stock exchange, although there was no impact on electronic trade, which makes up the vast majority of deals.