Using `docker import` in `dockerTools.buildImage`?

I am trying to run openwrt in oci-container docker container on my nixos machine.

I have downloaded the rootfs.tar.gz of openwrt to my computer and try to use buildImage to convert it into a container.

However buildImage does not accept the rootfs.tar.gz.

Is there a way to build the oci-container from a rootfs.tar.gz?