(Sharecast News) - Shares in Carrefour tumbled on Wednesday, after the grocer warned that the riots and mass protests sweeping France would hit profits.

Posting an update on third-quarter trading on Tuesday, the supermarket chain said sales had sparked 2.3% on a like-for-like basis, including a 1.2% uplift in France across all formats. However, looking to the current quarter and Carrefour warned that "in light of the worsening social and security situation", both consumer trends and operating conditions had deteriorated.

Protests by French students about the underfunding of schools and the cost of living have been hijacked by rioters, who have looted thousands of businesses across the country and set buildings on fire. Earlier this week the government was forced to impose overnight curfews in parts of central Paris and other cities in an attempt to halt the violence.

Political opponents on the left and right have blamed each other for the unrest.

Carrefour said it had been forced to scale back opening hours because of the curfews, while security and logistics costs have spiked alongside a slump in footfall. As a result, it now expects annual growth in its operating margin of between 0 to 15 basis points - compared to previous guidance for growth of at least 25bps - and cut guidance for adjusted earnings per share growth to "stable to slight". It had previously expected high single-digit growth.

As at 1045 BST, the Paris-listed stock had tumbled 14%.

Alexandre Bompard, chief executive, called the current situation "unprecedented" and said a "significant" number of Carrefour stores in urban areas had been affected.

He continued: "There is a high degree of uncertainty regarding consumer spending trends and the conditions under which our stores will be able to open. As we enter the critical end-of-year period for the retail sector, this situation is having a significant impact on consumer spending - which is already under pressure from rising energy costs - and is affecting the operations of our stores."