The ISEQ index of Irish shares plunged after confirmation of the first foot-and-mouth disease outbreak in the State compounded weakness in world equity markets.
Dealers reported panic selling across the board although food stocks took the biggest hit.
One dealer said: "It's ridiculous. We're seeing stocks dumped that are very unlikely to be impacted by all this."
The ISEQ was down 5.2 per cent or 278 points at 5,040.25 points - its lowest level since the beginning of August 2000. Losers outnumbered gainers 50 to five.
The Dublin market had been around 2 per cent lower before the news struck due to overnight falls on Wall Street and another slide by London's FTSE 100 index.
Among food stocks both Glanbia and Golden Vale lost 22 per cent after the Government imposed a ban on all animal product exports.
Tourism related-stocks such as low-cost airline Ryanair and hotel group Jurys Doyle also moved lower.
"It's just bad sentiment right across the ISEQ," said Mr Tom Kehoe, equity analyst at stockbrokers Dolmen Butler Briscoe. "It's the last thing the Irish market needed."
He said financial stocks such as Bank of Ireland and Allied Irish - both of which fell by over 6 per cent - were affected in large part by overseas weakness.
Heavyweight pharmaceutical company Elan, whose weighting accounts for around 25 per cent of the overall index, dropped over 5 per cent to 52.50 euros.