First install qemu-utils package, then you can use the following command:

qemu-img convert -cpf vmdk -O qcow2 {source}.vmdk {destination}.qcow2

The above command will convert from vmdk (VMWare) to qcow2 (KVM/QEMU).

• -c Creates a Compressed Output (Thin)
• -p Shows the progress
• -f Defines the input format (vmdk in this case)
• -O Defines the output format (qcow2 in this case)

The qemu-img command also supports vhd and vhdx for Windows Hyper-V as well as vdi for VirtualBox.