Spanish authorities were yesterday investigating a package containing a suspicious substance received at Madrid's central post office, where workers were examined for possible harmful effects.

A spokesman for Madrid's emergency services said firemen, ambulances and a specialist police unit had cordoned off the area and had decontaminated people as a precaution, but that all 23, including post office staff and customers, were well.

The suspicious package was reported early yesterday. It could take several days for investigators to determine the nature of the substance and whether it was a false alarm, the emergency spokesman said.