在Nginx的官方wiki中如下描述
The alias directive cannot be used inside a regex-specified location. If you need to do this you must use a combination of rewrite and root.

在实际使用中alias下面的php返回404,而html确可以正常显示,解决方法如下

location / {
root /opt/www/htdocs/www;
index index.php index.html index.htm;
}

location /bbs/ {
alias /opt/www/htdocs/bbs/;
index index.php index.html index.htm;
}

location ~ ^/bbs/.+.php$ {
root /opt/www/htdocs;
rewrite /bbs/(.*.php?) /$1 break;
include conf/fcgi.conf;
fastcgi_pass 127.0.0.1:10080;
fastcgi_index index.php;
fastcgi_param SCRIPT_FILENAME /opt/www/htdocs/bbs$fastcgi_script_name;
}

即用root加rewrite替换alias

来源:http://blog.tcisv.cn/index.php/2009/06/phpfastcgi%E5%9C%A8nginx%E7%9A%84alias%E4%B8%8B404%E7%9A%84%E8%A7%A3%E5%86%B3%E6%96%B9%E6%A1%88/