Demolition crews have begun tearing down two century-old buildings in the heart of the downtown district that were gutted last week by a fire that officials say was deliberately set.

The work began Saturday as wreckers tore down chunks of the red-brick Cressey and Kora buildings on Lisbon Street.

The crews from Costello Dismantling planned to return Tuesday to complete the demolition of the two buildings and to tear down the neighboring Greely and New England Furniture buildings.

The decision to move quickly with the demolition came after engineers and firefighters warned that the Cressey and Kora buildings were in danger of imminent collapse as their floors pancaked, leaving only the brick shells standing.

The Cressey, Kora and Greely blocks, named for their builders, were erected around 1895 as Lisbon Street's rapid development coincided with a boom in Lewiston's industrial economy that centered around its mills, said Douglas Hodgkin, a retired Bates College history professor.

The buildings' brickwork and granite facades were typical of the era's ornate Victorian architecture, Hodgkin said. He termed the Tuesday night fire a tragedy that would leave a "big hole in the streetscape."