start a process on cmd without waiting it (php)

I have to start a NodeJS server from my script in php without waiting it. To get started the NodeJS server I use...

$command = "cd /d " . $row["pathServer"] . " && node server";
exec($command, $output);

but it doesn't work because the webserver wait that the command finished. How can I separate the two process?

Thanks

via Max Valle