When shall a applicant request the priority right and how to request?

The article 30 of the Patent Law of PRC regulates that any applicant who claims the right of priority shall make a written declaration when the application is filed, and submit, within three months, a copy of the patent application document which is first filed; if the applicant fails to make the written declaration or to meet the time limit for submitting a copy of the patent application document, the claim to the right of priority shall be deemed not to have been made.