Reverse proxy with sub-directories using nginx and nodejs

I am having trouble setting up reverse proxy with nginx forwarding requests to node sitting a the back end. My nginx conf file is :

 server{
    listen 80;
    server_name 192.168.50.176;



location /stretch {
    rewrite /stretch/(.*) /$1 break
    proxy_pass http://localhost:3000/;
    proxy_redirect off;
    proxy_set_header Host $host;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
} 

Without subdirectories it works just fine.The below config works :

server{
    listen 80;        
    server_name 192.168.50.176;



location / {
    proxy_pass http://localhost:3000/;
    proxy_redirect off;
    proxy_set_header Host $host;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
}