Nearly 30,000 German dairy farmers halted milk deliveries to retailers on Wednesday on the second day of their strike, according to the European Milk Board, based in the western German city of Hamm.
It said deliveries dropped by some 60 percent in Switzerland's Zurich region and in the Netherlands, where the Dutch Dairymen Board urged its 4,000 producers to "keep milk on the farm."
Austria's IG Milch dairy association weighed in with a call on the country's 43,000 dairy producers to halt deliveries in protest at the milk price. "We urge all producers to cease delivery to dairy factories completely from Thursday," said the federation's president, Ewald Gruenzweil.
He warned consumers, especially hospitals, kindergarten nurseries and schools, to start stocking dairy products. "We're predicting (supermarket) shelves to empty rather quickly as people start hoarding, following this determined action in Germany and other European countries," Gruenzweil added.
Germany's BDM dairy federation, which represents almost half of the country's producers, said it had also received "declarations of support" from Belgium, Luxembourg and "parts of France."
"I expect more countries to join the strike," deputy president Stefan Mann told the Frankfurter Rundschau daily newspaper.
The strike in Germany, Europe's biggest milk producer, began on Tuesday as farmers heeded a call by the BDM to stop supplying milk in order to force up prices that are currently hovering between €0.28 and €0.34 ($0.43 - $0.53) per litre (2.2 pints to the litre).
"We plan to decrease the flow to the food industry further still in coming days and then supermarkets will start feeling the pinch," said Hans Foldenauer, a spokesman for the BDM.
Germany opposed a decision by European Union agriculture ministers in March to allow a bloc-wide increase in production of two percent as part of a larger plan to phase out dairy subsidies by 2015.
Agriculture Minister Horst Seehofer warned there was a risk the move could lead to "new milk lakes and butter mountains," a reference to surplus production in Europe triggered in 1984.
Milk prices increased by an average 8.1 percent in the EU last year but have slipped back since reaching a peak in the autumn.
The BDM said that milk prices agreed between suppliers and supermarkets have fallen by as much as €0.15 per litre compared to last year, while dairies' operating costs have risen. It is demanding that the milk price be pushed up to €0.43 per litre.
The Swiss farmers' trade union Uniterre said some 100 dairy producers in the west of the country voted Wednesday in favour of joining a delivery strike in the German-speaking part of Switzerland in support of German producers.
"We have been negotiating about the milk price for years without any success. So we can only conclude that a strike is the only way forward," a union representative told the ATS news agency.
Switzerland's Big-M union said the 200 producers in the Zurich region had delivered virtually no milk on Wednesday.
The milk price protest seemed set to spread to Romania next week. Romanian agricultural trade union Agrostar said dairy farmers would stage a three-day picket outside the French embassy in Bucharest and the headquarters of dairy company Danone to demand better prices for their milk.