Which is fastest way to get 10 lines randomly inside a file with 10.000 lines?

Which is fastest way to get 10 lines randomly inside a file with 10.000
lines?

I have a file with ~ 10.000 lines inside. I want every time user access my
website, it auto pick 10 lines randomly among them.
Code I currently used:
$filelog = 'items.txt';
$random_lines = (file_exists($filelog))? file($filelog) : array();
$random_count = count($random_lines);
$random_file_html = '';
if ($random_count > 10)
{
$random_file_html = '<div><ul>';
for ($i = 0; $i < 10; $i++)
{
$random_number = rand(0, $random_count - 1); // Duplicate are
accepted
$random_file_html .=
'<li>'.$random_lines[$random_number]."</li>\r\n";
}
$random_file_html .= '</ul>
</div>';
}
When I have < 1000 lines, every things is ok. But now, with 1000 lines. It
make my website slow dow significantly.
That I'm thinking to other methods, like:
Divide file to 50 files, select randomly them, then select 10 lines
randoms inside the selected file.
-- or --
I knew total lines (items). Make 10 numbers randomly, then read file use
$file = new SplFileObject('items.txt');
$file->seek($ranðom_number);
echo $file->current();
(My server does not support any type of SQL)
Maybe you have other methods that best suit for me. What is best method
for my problem? Thank you very much!