1. There is 2 possibilities for your parcel. Either the parcel is going to a different City where they can fly to Portugal or your parcel has difficulty passing the export customs scan. Here is the full tracking of your parcel:

China Post Register Air Mail Tracking System
Parcel No.RK500822699CN tracking result
2016-08-24 17:12:27.0 镇江丹阳city Post Office parcel 局 received
2016-08-24 17:23:03.0 镇江丹阳city Post Office parcel 局 customs scan
2016-08-25 08:29:52.0 leaving 镇江丹阳city Post Office parcel 局 ，next station 镇江
2016-08-25 14:39:19.0 Nanjing Transit Station export security scan
2016-08-25 17:20:17.0 Nanjing Transit Station export customs scan (domestic transit )

2. May I suggest your read this:

What is the status of “Export Customs Scan” ? How long it will take?

http://track-chinapost.com/China_Post_Arrival_Time_Stat.php

3. May I suggest also you contact the seller so he can call China Post about your parcel. Tell him you are worry about your parcel being in Nanjing Transit Station export customs scan for so long. Please provide him the above tracking so he understand what you are talking about.

Hope this help.