Asda chief Andy Clarke to be replaced by Sean Clarke

Andy Clarke has led Asda for six years

Asda owner Walmart has said the UK supermarket's chief executive, Andy Clarke, is stepping down to be replaced by the head of Walmart's Chinese business, Sean Clarke.

Walmart said Sean Clarke's experience would allow him to "reposition the business" in a competitive market.

Sean Clarke started his retail career at Asda in 2001 and has also worked for Walmart in Japan and Canada.

Asda has now reported seven straight quarters of declining sales.

The appointment comes as a surprise after Andy Clarke said last week in an interview that he would be succeeded by Roger Burnley, who is joining Asda from Sainsbury's.

Mr Burnley has been named as Asda's deputy chief executive and chief operating officer.

David Cheesewright, president and chief executive of Walmart International, said Mr Burnley was "a top talent and a future CEO".

Competitive marketplace

Andy Clarke has served as Asda's chief executive for six years in an increasingly tough market.

Last month, the retailer said like-for-like sales in the first quarter of the year fell 5.7% in the face of "fierce competition".

Analysis, Emma Simpson, business correspondent

It seems that Andy Clarke is going earlier than he anticipated. Although he moved faster than his main rivals to try to counter the threat of the discounters, Asda has been haemorrhaging sales for the last seven quarters. Mr Clarke promised to narrow the price gap but the discounters are still the cheapest grocers on the high street meanwhile Tesco, Sainsbury's and Morrisons have all upped their game, leaving Asda trailing behind. Sean Clarke is described as a rising star within Walmart, someone who is experienced in dealing with major structural change. Clearly Walmart thinks a fresh pair of eyes is now needed to revive Asda's performance and he's been parachuted in.

Parent company Walmart will hope his successor can grab back some of their market share.

Mr Cheesewright said: "Sean is one of our most experienced global executives, and through his leadership we will build upon the momentum of Project Renewal to reposition Asda in a very competitive market place."

Project Renewal is a programme designed to overhaul Asda's product range, modernise its 95 largest stores and reduce costs.

Asda is attempting to recoup sales by narrowing the price gap with the discounters and widen its price advantage over its three biggest rivals.

All of the four major UK supermarket chains - Tesco, Sainsbury's, Asda and Morrisons - have been engaged in a long-running price war as part of an attempt to slow gains in market share by discounters such as Aldi and Lidl.

Last week, online retailer Amazon launched its fresh grocery service in the UK, adding to competition in the sector.