* Euro tumbles to one year low against dollar
* Stocks slide as materials, financials hit
* Oil extends losses, down below $82
By Elaine Lies
TOKYO, April 28 (Reuters) - The euro tumbled to a one-year low against the dollar and Asian stocks fell after downgrades of Greece and Portugal's credit ratings set off a flight to safety on fears the euro zone's debt problems were spreading.
Oil extended losses to below $82 and metals prices were hit after ratings agency Standard & Poor's slashed the sovereign ratings of Greece to junk status and downgraded Portugal.
* Standard & Poor's downgraded Greece into junk territory on concerns about its ability to implement the reforms needed to address its high debt burden, cutting its rating a full three notches to BB-plus, the first level of speculative, or "junk," status.
* On Portugal, Standard & Poor's cited concerns about the country's ability to deal with high debt levels given its weak economic outlook, cutting the rating by two notches to A-minus.
* On Wall Street, stocks had their worst day in nearly three months, with all three major indexes down about 2 percent. The CBOE Vix volatility index, Wall Street's barometer of investor fear, jumped about 31 percent.
* The euro hit a one-year low against the dollar, falling as far as $1.3144 on trading platform EBS, after tumbling nearly 2 percent on Tuesday for its biggest one-day percentage loss in about a year. It later crawled higher, edging up 0.2 percent to $1.3177.. It rose the same amount against the yen to 122.62 yen
* Japan's benchmark share index Nikkei fell 2.8 percent, with metals and exporters hit especially hard after climbing earlier this week. Honda Motor Co skidded 3.2 percent.
* Australian shares at one point fell 1.8 percent to a six-week low, with banks and miners hit hardest. The benchmark S&P.ASX 200 index lost 1.7 percent.
* Materials and financial shares were battered across the region, pushing the MSCI index of shares outside Japan down 1.5 percent.
* Crude oil fell under $82, pressured by statistics showing a surge in U.S. crude stockpiles. NYMEX crude for June delivery lost 51 cents to $81.94 a barrel after falling nearly $2 the day before as the Greece and Portugal downgrades prompted market players to pull cash out of energy markets.
* London copper and aluminium futures fell, with other metals also sliding. Gold edged down on Wednesday after surging to a 2010 high the previous day, with spot gold at $1,166 by 0117 GMT. (Editing by Tomasz Janowski)