* Oil prices plunge 30%
* Russian rouble loses almost 10% against euro
* S.African rand tumbles to 4-year low as Eskom cuts power
* Oil importer India's rupee flat as it benefits from oil slide
* MSCI's EM index on track for worst day in 4-1/2 years
By Susan Mathew
March 9 (Reuters) - Currencies of oil-exporting countries Russia and Mexico sank more than 7% on Monday as crude oil lost more than a quarter of its value after Saudi Arabia launched a price war with Russia, adding to fears of a global recession.
Stocks across emerging markets were also deep in the red, as global investor confidence was shattered by the double whammy of the sharpest one-day fall for oil in 29 years and the rapid spread of the coronavirus outside China.
Saudi Arabia slashed its official crude selling price and set plans for a dramatic increase in production following Russia's refusal to make a further steep output cut to stabilize oil markets.
Saudi stocks plunged as much as 9% to their lowest since September 2016, with Saudi Aramco down 10%.
The rouble slumped as much as 10% against the euro to hit its lowest level since the first quarter of 2016. Russian authorities were quick to respond to the currency's fall on Monday, a non-working day. The central bank suspended its daily purchases of foreign currency for state reserves for 30 days.
Mexico's peso also slid to its lowest level since 2016 as investors worried about the impact of the price cut on heavily indebted state oil firm Pemex.
"We had expected rate cuts in Russia and Mexico next week, but these currency falls probably take those off the table," said William Jackson, chief emerging markets economist at Capital Economics in London.
"There seems to be no substantial change in Saudi's oil policy so far which means oil prices will remain low for a while."
South Africa's currency tumbled to four-year lows after state power utility Eskom said it would resume nationwide power cuts in Africa's most industrialized nation on Monday.
The rand dropped up to 7.6%, before cutting some losses to trade down 2.3% at 16.03 to the dollar.
A massive drop in yields quashed the dollar, helping cap losses in some Asian currencies. The Indian rupee declined the least among emerging market peers as the net importer was one among the few beneficiaries of the oil slump.
The MSCI index of developing world equities lost 4.4%, giving up its gains from last week when sentiment had been lifted by policy easing from the U.S. Federal Reserve and some emerging market central banks to stem the economic damage from the health crisis.
Markets have fully priced in an additional 75 basis points cut by the Fed next week as the number of global infections surpasses 100,000, even as analysts question the extent to which monetary easing will be meaningful in reviving supply chains.
Data from Institute of International Finance showed emerging markets are in the middle of their worst outflow period on record as portfolio managers pulled around $30 billion in about 45 days.
Asian shares gave up between 3% and 6%, taking an index of regional equities excluding Japan down 5% to its lowest in six months.
Shares in Turkey and South Africa lost between 3% and 6%. Polish stocks crumbled 6.5% to their lowest since 2009, while Hungarian stocks slumped 8%.
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Reporting by Susan Mathew in Bengaluru; Editing by Shailesh Kuber