Android SDK Manager - Loading SDK component information failed

Using Visual Studio 2017 ( 15.9.22) and trying to open Android SDK Manager under Tools->Android gets the message "Loading SDK component information failed.Please retry" 

The output window in Visual Studio IDE shows the following message

ValidateAndroidSdkLocation: `C:\Program Files (x86)\Android\android-sdk`, result=True
 ValidateAndroidNdkLocation: ``, result=False
[I:]:                     Looking for Android NDK...
[D:]:                     ValidateJavaSdkLocation: `C:\Program Files\Android\jdk\microsoft_dist_openjdk_1.8.0.25`, result=True
[I:]:                     Found Xamarin.Android 9.1.7.0

From the above message its looks like there is some issue with AndroidNdklocation. Where is Android NDK location and how do I set it?