Errors with PHP 7.1

[04-Mar-2017 07:01:50 Australia/Sydney] PHP Fatal error:  Uncaught Error: Class 'mysqli' not found in /home/example/public_html/perch/core/lib/PerchDB_MySQLi.class.php:27
Stack trace:
#0 /home/example/public_html/perch/core/lib/PerchDB_MySQLi.class.php(76): PerchDB_MySQLi->open_link()
#1 /home/example/public_html/perch/core/lib/PerchDB_MySQLi.class.php(300): PerchDB_MySQLi->get_link()
#2 /home/example/public_html/perch/core/apps/content/PerchContent_Pages.class.php(279): PerchDB_MySQLi->pdb('/index.php')
#3 /home/example/public_html/perch/core/apps/content/runtime.php(215): PerchContent_Pages->find_by_path('/index.php')
#4 /home/example/public_html/_global/global.inc(4): perch_pages_title(true)
#5 /home/example/public_html/_global/global_home.inc(1): include('/home/example/...')
#6 /home/example/public_html/index.php(1): include('/home/example/...')
#7 {main}
  thrown in /home/example/public_html/perch/core/lib/PerchDB_MySQLi.class.php on line 27