"Ultimate Guide: Obtaining a Chinese No Criminal Record/Conviction Certificate for a Portuguese Visa as a Nigerian Living in China"

1. Grab your passport (all passports used in China).
2. As a student: Get a letter of good conduct from your school. It will include your studentship, passport number, and good conduct statement. As a Worker: Go to the Police station and request one. A new update says you get one at the Public Security Bureau, especially for people in big cities.
3. When you apply at the PSB, you (or your representative) must bring All of your original passport(s) (your current passport and any other passports that have your Chinese visa). Your Residence permit and Work permit. A letter from your work or university/school where you worked or studied while you were in China and an employment contract. Applicable fees
4. Take the No Criminal Record Certificate (NCRC) written in Chinese to the Notary Public in your city.
5. You must bring your certificate of No Criminal Convictions from the Public Security Bureau office to the Notary Public Office to get a notarised translation. You (or your representative) must bring Your original passport (with your original Temporary Residence Card or Temporary Residence Permit). Your original certificate of No Criminal Convictions from the PSB.
6. At the Notary, they will ask you what country needs it, its purpose for notarization, and how many copies. You can request it in English and Portuguese, but Portuguese is more important. Then you will be asked to sign many authorization documents, and your photo or video might be taken. Pay for the documents and wait for the collection date. You might request it to be sent by mail.
7. Make sure the notarised copy includes your name, date of birth, passport(s) number(s), and it says specifically that "you are not a criminal in China." It also comes with a blue and red signature and stamp.
8. You will take this to the Ministry of Affairs (MFA) in your state of the next big city in your province if your city is small.
9. MFA takes your notarised NCRC for authentication and then forwards it to the Portuguese Consulate. Depending on your city, it takes about 6–7 weeks and isn't cheap.
10. If you don't get notified after 6–7 weeks of the pickup date, return to the MFA and pick it up.
11. After this, go to the visa submission center (VFS)

If you live outside China:

No other option exists; you must nominate a representative to finish this job.

Using a representative: most places in China will allow a representative to apply for a police certificate on your behalf. To nominate a representative, give the person a signed, notarized authorization letter.

General Documents

1. Current passport
2. Any prior passport that contains pages with China entry and exit stamps and residence permit(if applicable).
3. Copy of temporary residence registration.
4. A power of attorney if a representative makes the application on your behalf(if applicable).
5. School/employer letter confirming no criminal record(some cities may apply).

Source: https://www.mapleleafnotary.cn/zhong-guo-wu-fan-zui-zheng-ming/