Nearly 300 children in the nation's orphanages over the past two years could not be put up for adoption because consent from their biological parents could not be obtained, a welfare ministry survey showed Thursday.

Under civil law, consent is required by the "special adoption" guidelines used to grant a child the same legal rights as the adopting parents' biological children under the national family registry system.

The ministry plans to consider measures that make it easier to deal with consent problems, whether the biological parents are reluctant to grant approval or whether they cannot be found, ministry officials said.