The European Central Bank today ramped up its stimulus for the moribund 19-nation single currency bloc by announcing that it will buy 60 billion euros (£46 billion) of assets every month.
ECB president Mario Draghi told a press conference in Frankfurt that the purchases were an expansion of an existing policy.
He also said the central bank would start a widely-anticipated programme of buying government bonds, along the lines of the quantitative easing (QE) that has already been pursued in the US and UK. This will begin in March.
Mr Draghi said the wider asset purchase programme was intended to carry on until September 2016 - and "in any case be conducted until we see a sustained adjustment in the path of inflation".
It comes as the eurozone is facing stagnation with inflation at minus 0.2%, threatening a damaging deflationary spiral.
The scale of the asset purchase scheme over 19 months would amount to 1.14 trillion euros (£870 billion).
Mr Draghi said purchases will start to include the purchase of bonds "issued by euro area governments and agencies and European institutions" from March.
John Cridland, director-general of the CBI, welcomed the move.
He said: "At the moment, flagging eurozone economies are dragging on UK and world growth.
"Quantitative easing will give the eurozone recovery a much-needed boost, which should also have a positive economic effect in the UK.
"To gain maximum effect though, this action must go hand-in-hand with structural reform. France needs to work with the business community to modernise its labour rules and Germany should invest more in infrastructure."
John Longworth, director general of the British Chambers of Commerce said: "The ECB has to act to prevent the Eurozone from falling into an even more dangerous situation, but the ECB's proposed QE programme may be too little too late, given the size of the challenge.
"The ECB's QE programme is unlikely to solve the fundamental challenges facing the eurozone, which needs sweeping structural changes to return to health.
"UK businesses will continue to trade with Europe - but only a broad-based recovery in the Eurozone would enable them to achieve their export ambitions in continental markets."
Mr Draghi's announcement is seen as a last-ditch measure to save the eurozone.
Pressed on whether there was a "plan B" should inflation fail to tick up, he said: "We just present a plan A. We have a plan A, period."
Government bonds will be bought in proportion to the bloc's capital key - the size of the ECB's contributions from each national central bank.
It means the largest economies, from Germany downwards, will see more of their bonds purchased than their smaller peers.
Mr Draghi said that "additional eligibility criteria" would apply in the case of countries under an EU/IMF bailout programme - currently Greece and Cyprus.
Kathleen Brooks, research director at Forex.com, said the announcement did not amount to "full-blown QE".
That was because only 20% of the programme would be subject to "risk-sharing" where all members of the eurozone would share losses in the event of a debt default on the bonds, with national central banks taking on 80%.
It means that should the assets they buy lose value, national central banks - which under the single currency no longer have the power to print money - would have to rely on a bail-out from their governments, said Miss Brooks.
"This is probably the work of the Bundesbank, who don't want the German taxpayer on the hook for bad loans from its neighbours.
"This highlights the political risks of QE in the Eurozone. Today's decision actually drives the currency bloc apart, not closer together."
Miss Brooks said it meant the programme was "nothing like" what had been done by the US Federal Reserve, the Bank of England or Bank of Japan.
The QE amounted to only 200 billion euros (£150 billion) because only that proportion would see risk shared, she added.
Chancellor George Osborne told Bloomberg TV: "I think this is welcome action from the European Central Bank but action from a central bank is necessary, but not sufficient for a European recovery.
"We want to see this accompanied by clear plans to make the European continent more competitive to back business in Europe, to create jobs, and to make sure public finances are in order."
The pound climbed to a new near-seven year high against the euro, topping 1.32 for the first time since February 2008 though it later edged a little below this level.
The effect will be welcome for UK holidaymakers visiting Spain and France but less so for British firms exporting to the continent as their products will become relatively more expensive for European customers.
Stock markets were also ahead on today's much-anticipated announcement though much of the reaction had already been factored in to prices.
The ECB had been under pressure to act as the eurozone faced zero growth and deflation, accelerated by the slide in the oil price. Mr Draghi had pledged two and a half years ago to do "whatever it takes" to hold the eurozone together.
Interest rates had already been slashed to 0.05%.
ING Bank's Carsten Brzeski said: "Today's QE announcement is historic but it was also the ECB's last trump card. There are no more hidden aces."
A spokeswoman for 10 Downing Street told reporters: "We think it is important that the eurozone take the necessary action to get the euro area growing, while at the same time recognising that euro area countries need to tackle their fiscal challenges and also look at necessary structural reforms.
"In the UK a key part of our economic plan has been monetary activism, alongside fiscal responsibility and structural reform. The UK economy is one of the fastest growing in the G7 at the moment."