Riyadh: Saudi Arabian shares tumbled the most in more than six weeks, led by Saudi Basic Industries Corp and Samba Financial Group, as President Barack Obama's plan to rein in banks sent shares tumbling across the globe.

Saudi Basic Industries Corp, the world's largest petrochemical maker known as Sabic, was poised for its lowest close in more than a week, while Samba fell the most in six weeks. The Tadawul All Share Index slipped 1.4 per cent to 6,292.86 at 1.13pm, the biggest decline since December 9.

The decline is due to "the effect of the global markets," Raj Sinha, head of equity research at HSBC Saudi Arabia, said in an email. "Earnings season was fine, but there wasn't a case of overall positive or overall negative, so global markets are a key driver today."