Intel X86 emulator accelerator (HAXM installer) VT/NX not enabled

From the Intel Instructions

"The SDK Manager will download the installer to the "extras" directory, under the main SDK directory. Even though the SDK manager says "Installed" it actually means that the Intel HAXM executable was downloaded. You will still need to run the installer from the "extras" directory to finish installation.

Extract the installer inside the "extras" directory and follow the installation instructions for your platform."

Go to the SDK manager in your IDE and install the latest "Intel HAXM" and start the emulator.

If it is throwing the error as:

Starting emulator for AVD 'X86'emulator: ERROR: x86 emulation currently requires hardware acceleration!Please ensure Intel HAXM is properly installed and usable.CPU acceleration status: HAX is not installed on this machine (/dev/HAX is missing).

It means that some hardware graphical features are to be assigned.So to overcome this problem just go to the path where you have your Android SDK installed.

Windows

C:\Android\SDK\extras\intel\Hardware_Accelerated_Execution_Manager

There you can find the file intelhaxm-android.exe.

Mac OS X

On macOS there is a IntelHAXM_X.X.X.dmg file, mount it and you'll find an mpkg-file.

Install the file and restart all the applications using android emulator such as android studio, cmd, etc.

Now try to open the emulator it will work fine

You might be running an older version of Intel HAXM (or haven't installed it at all). Go to https://software.intel.com/en-us/android/articles/intel-hardware-accelerated-execution-manager and download/install the latest Intel HAXM package for MAC OS X.

EDIT: according to https://software.intel.com/en-us/forums/topic/506790 you should also make sure that Virtual PC/Parallel/VMWare is not running.