At least a dozen people remained quarantined on the fourth floor of the state Capitol shortly after 4:30 p.m., a state police spokesman said Thursday afternoon.

They were quarantined after the govenror’s office received a suspicious envelope filled with a powdery white substance. Gov. Bill Richardson is not in the Capitol but is in Washington today, his spokesman, Gilbert Gallegos, said. It is unclear if Lt. Gov. Diane Denish is among those quarantined, said Lt. Eric Garcia of the New Mexico State Police.

Authorities initially evacuated the fourth floor of the Capitol but then expanded that order to the entire building for the safety of the public, Garcia said. The Capitol remains evacuated.

In addition, authorities shut down Old Santa Fe Trail, one of the thoroughfares that runs by the Capitol.

The National Guard will test and identify the substance at the Capitol, Garcia said.

The Governor’s Office and the Lt. Governor’s Office were initially evacuated at 2:15 p.m. following the discovery of an unidentified, white substance.

The decision was made later to evacuate the entire building, Garcia said.

The letter the governor’s office received appears to have been part of a coordinated mail spree. Governors of several states received the letters. Initial tests found the substance contained in the letters to be not harmful.