Migrate users with via mongoexport/mongoimport from one db instance to another

Hi
We are moving the databases from one data center to another. As part of this , we are setting up new mongo replica set in new DC and copying the databases using mongodump/mongorestore. We are also trying to retain the same users/password as part of migration, for which we exported admin db system.users collection, while import it is failing saying system.users doesnt exist. Tried to perform manual insert, but the password is not working.
Please assist how we can transfer users and keep the same password in the new instance.