Fatal Error: 'SQLite3' is an unknown class name - PHP - SQLite

Question

I have installed sqlite db on my server and can access the tables and data without any issues. But when i try to access it through a PHP script, I get an error - Fatal Error: 'SQLite3' is an unknown class name. Is anyone aware of this error and reasons for it to occur?

<?php header('Access-Control-Allow-Origin: *');

echo "Connected successfully";

$db=new SQLite3('/npu/dex/database/npu.sqlite3');   // Error : Fatal Error: 'SQLite3' is an unknown class name
echo "SQLite 3 supported.";


?>