Michoacan authorities had said late on Friday that the four inmates, jailed for kidnapping and racketeering, took six defence attorneys captive, but by early on Saturday they said the number of hostages was closer to a dozen.
Police and army troops were on watch outside the facility, but as of midday on Saturday, they had not moved in.
The kidnappers were demanding a car to escape, and family members were trying to convince them not to attempt to flee, authorities said.

Copyright AFP (Agence France-Presse), 2006