Qt Creator: Project ERROR: You need to set the ANDROID_NDK_ROOT environment variable

I've just installed Qt 5.12.7 with offline installer, and having previously setup the Android SDK and NDK, along with Java 8, when starting Qt Creator for the first time the following messages appeared under tab "6 General Messages":


Project ERROR: You need to set the ANDROID_NDK_ROOT environment variable to point to your Android NDK.
Could not read qmake configuration file /opt/Qt5.12.7/5.12.7/android_armv7/mkspecs/android-clang/qmake.conf.

Project ERROR: You need to set the ANDROID_NDK_ROOT environment variable

If you received such error message when build a Qt application for Android within Qt Creator, the simple solution is to export the ANDROID_NDK_ROOT environment variable pointing to the folder where you have uncompressed the Android NDK bundle. Then run Qt Creator again and the build should continue without issues.