Trucks deliberately slowing down to a snail's pace clogged highways across Spain on Tuesday as drivers protesting rising fuel costs pressed on with a transport strike that has disrupted supplies of food, fuel and other goods.

Three auto plants _ one each from Nissan, Mercedes Benz and SEAT _ said they were suspending operations because of a lack of spare parts. And some gasoline stations in Madrid and the northeastern Catalonia region already have run out of fuel.

Vendors warned of shortages in fruit, vegetables and meat this week at Madrid's sprawling wholesale market, Mercamadrid, if the strike continues.

Fishermen also have been on strike since May 30 to protest rising fuel costs, which have especially hurt Spain's independent or self-employed contractors amid an overall economic slowdown in Spain.

Mercamadrid on Tuesday took in 10 truckloads of fish _ compared with 90 on a normal day, said Manuel Pablos, president of an association of fish merchants.

The combination of the two strikes "is making these days very grim," he said.

Traffic to and from Madrid, Barcelona, Seville, Alicante and other cities was backed up behind trucks, the Interior Ministry's traffic division said. Trucks also blocked the Junquera border crossing with France for a second day, allowing only cars through.

The ministry opened up three toll roads to ease access to Madrid.

The striking truckers are demanding minimum, guaranteed haulage rates to offset rising fuel prices and enable them to compete with large trucking companies.

The government was meeting Tuesday with the truckers' representatives, but it has said setting guaranteed rates would violate the principle of free market competition.

The strike is the most serious labor unrest facing Prime Minister Jose Luis Rodriguez Zapatero since he came to power in March 2004.

Spain's economy has slowed after a decade-long boom in the real estate sector came to a halt. The government in April lowered its 2008 economic growth forecast to 2.3 percent, from its previous estimate of 3.1 percent.

Meanwhile, a similar truckers' protest was taking place in Hong Kong, with truck drivers in a go-slow strike to disrupt traffic and protest rising fuel costs.

About 300 marched Tuesday to Hong Kong's government headquarters and demanded that fuel taxes be slashed, according to government-run broadcaster RTHK.

Light, sweet crude for July delivery was at $136.61 a barrel on the New York Mercantile Exchange on Tuesday.