AFP - A Finnish dock workers' strike that has crippled the export-reliant Nordic country's foreign trade entered its fifth day Monday, with major companies saying they were forced to temporarily halt operations.

The key forestry industry was one of the worst-hit, with the world's largest magazine paper maker UPM-Kymmene announcing it had halted paper production at its sites in Rauma, Kaukas and Kaipola.

While it aimed to keep "at least one production line" operating at its other paper mills this week, it said in a statement production would be curtailed further from Wednesday.

Stainless steel maker Outokumpu also said its deliveries and raw materials supply were affected, and it would have to halt the production of stainless steel and ferrochrome at its plant in Tornio "within a week".

All of Finland's commercial ports -- which handle around 80 percent of its foreign trade -- ground to a halt Thursday morning as some 3,000 stevedores walked off the job when collective labour deal talks broke down.

Politicians, including Prime Minister Matti Vanhanen, have joined industry leaders in calling for a quick resolution to the dispute, insisting the ports closure was dealing a further blow to the country's recession-hit economy.

"The effects (of the strike) can be measured in tens and even hundreds of millions of euros," senior economist Simo Pinomaa from the Confederation of Finnish Industries (EK) told AFP.

"Some of the lost foreign trade income can be recovered if the strike ends quickly... but if it is prolonged, export income will be lost permanently," he said.

One of the "more serious long-term consequences," he said, was that Finland's reputation as a reliable supplier would be damaged.

"Even a few days are too many. If the strike lasts for more than a week, we will start to be in serious difficulties," he said.

Finland's economy relies heavily on exports and, using 2009 figures, EK estimated the country was losing 110 million euros (150 million dollars) in exports and around 90 million euros in imports every day of the strike.

"It is clear that in this situation, where the economy is just starting to recover and there is fierce competition for global market shares, there can be permanent losses in terms of clients," Pinomaa said.

In a bid to end the strike, National Conciliator Esa Lonka has called employee and employer representatives to meet Tuesday.