Cooling tower of Doel's nuclear plant is pictured on Oct. 4, 2012 in Doel, north of Belgium. (Xinhua/Wu Wei)

BRUSSELS, June 25 (Xinhua) -- More than 50,000 people from Belgium, Germany and the Netherlands formed a human chain across the border triangle of the three countries on Sunday, to call on the Belgian authorities to close two nuclear reactors in Belgium.

Tihange 2 and Doel 3, were found have cracks in the walls of their pressure vessels, according to the Belgian news agency Belga.

The two large-scale nuclear power stations in Belgium, known as Tihange and Doel, have been in service since the mid-1970s.

Seven nuclear reactors are currently in service in Belgium, which produce 55 percent of the country's electricity supply, according to Electrabel, the company managing these reactors.

The Belgian government has vowed to phase out nuclear power completely by 2025.

The human chain on Sunday was jointly organized by Belgian, Dutch and German citizen initiatives, including Stop Tihange, End of the Nuclear and 113eweging.