[Refugees and migrants stand next to a border fence at the Greek-Macedonian border, after Macedonia closed its borders near the village of Idomeni]By Yannis Behrakis IDOMENI, Greece (Reuters) - Migrants cradling young children blocked a motorway in central Greece demanding onward passage to Macedonia on Wednesday, part of a growing bottleneck of refugees stranded by new border restrictions and closures across Europe. Reuters journalists saw other groups gathered at petrol stations and motels along the 530-km (330-mile) route from Athens to Macedonia, where guards opened the border for an hour on Wednesday morning, letting just 100 people through. Greece has protested against restrictions imposed by countries further north along the main land migration route into Europe, including along Austria's frontier with Slovenia and Macedonia's border with Greece.