Cloning database without dump/restore

Only port 5432 is opened in server. Database can cloned using pg_dup /
pg_restore
If server is located in internet this requires huge amount of time and
bandwidth.

How to clone database fast ?
How to create server side pl/pgsql script which use code like in
pg_dump/pg_restore and or in pg_migrator and clones existing database or
other idea ?

Andrus.