ISTANBUL  - Thirteen illegal immigrants suffocated in an overcrowded truck container and their bodies were dumped Wednesday in a field in Istanbul's outskirts, officials and media reports said. They were among 80 people from Pakistan and Myanmar who were crammed into the vehicle in the eastern province of Van for a 1,650-kilometre clandestine journey to Istanbul, Anatolia news agency quoted Istanbul Governor Muammer Guler as saying. "When the sweltering truck became unbearable, they began punching the driver's cabin and he stopped... It was determined that 13 people were dead, four were unconscious and 63 others alive," Guler said, relaying the accounts of passengers. "This is a tragic example of people smuggling," he said. The trafficking ring had sneaked the group to Van from neighbouring Iran, Guler said. Most of the dead were believed to be Pakistanis, the Hurriyet newspaper reported on its web site. Police were looking for the driver, who fled after dropping off the bodies as well as the surviving immigrants in a field in the Kucukcekmece district, on Istanbul's European side. The security forces sealed off the area, launching an operation to hunt down the immigrants who ran away, and a helicopter was helping in the search. About 50 migrants were rounded up and 10 of them were taken to hospital suffering from severe exhaustion and dehydration, reports said. Turkey lies on a major people-smuggling route from Asia to western Europe, and illegal immigrants are rounded up on a daily basis.