Concatenate 2 CLOB in oracle

SQL
====
Select  CONCAT(clob1, clob2) from table

PL/SQL
====
declare
  clob1 clob;
  clob2 clob;
begin
  clob1 := 'Clob1 ';
  clob2 := '+ Clob2';
  dbms_output.put_line(CONCAT(clob1, clob2));
end;