Vodafone is fighting to buoy its share price and has opted to take the drastic action of launching a massive share buy-back programme.

It has announced a surprise £1 billion ($2 billion) buy-back programme after its stock crashed on a weaker-than-expected trading update.

The company will now need shareholder approval for the buy-back, and will apply for this at its annual general meeting on 29 July.

Earlier on in the week, Vodafone shares slumped almost 14%, wiping nearly 11 billion pounds of its market value.

This came after the company admitted that its full-year revenue would be at the bottom of a previously stated forecast range.

"The board of Vodafone Group Plc has considered the market reaction ... and has decided to introduce a £1 billion share repurchase program with immediate effect", the world's biggest mobile phone group by revenue said in a statement.

"This action reflects the board's belief that the share price significantly undervalues Vodafone."

The day after the announcement (which was Wednesday), Vodafone's shares were 2.5% higher in early trading, valuing the company at £81 billion.