"We could be in a position where we already have all we need for our national consumption before we've even planted a single mealie next year," said a trader.
Farmers had ignored calls from producer body Grain South Africa to plant less and had sown 2.930 million hectares -- up from a January estimate of 2.895 million, the committee said.
"The acreage is up and we are expecting very good yields because of good rains in January and February," committee chairman Rodney Dredge told Reuters.
Farmers had planted 1.845 million hectares with white maize and 1.085 million hectares with yellow, he said. The 2005 harvest was estimated at 6.064 million tonnes of white maize and 4.195 million tonnes of yellow.
Prices have dropped from over 1,000 rand a tonne in November to close at 488.8 rand a tonne for March white maize on Monday after heavy rains last week and over the weekend. At these price levels, farmers say they may face bankruptcy.
Grain South Africa says farmers should band together to build a biofuel plant to mop up the surplus, but traders say this would take months to have any effect.
Traders say further falls are possible, with little demand in the rest of southern Africa after good rains. Neighbouring Zimbabwe is seen as needing some 600,000 tonnes of maize, but traders say it may lack the money to buy.
"All the news is pretty bearish at the moment," said another trader. "I think we could see March white go to 390 or lower."
Traders say the Crop Estimates Committee has traditionally been overly cautious in its early estimates, with the figure rising during the year, leaving some traders expecting a final crop in excess of 11 million tonnes.