Two migrants who hid inside an empty fuel truck have died after being hospitalised in northern Serbia, hospital staff said Thursday.
Four men, two believed to be from Afghanistan and two others were found unconscious inside the sweltering tank of the truck parked at a car wash near the city of Novi Sad on Tuesday.
They were suffering from hypoxia, or a lack of oxygen, and heat stroke.
A first man died on Wednesday and a second overnight, a hospital spokesman told AFP.
The two others remained in serious condition.
Serbia sits on the so-called Balkans route taken by hundreds of thousands of migrants between 2015 and 2016.
Although it was largely shut down in March 2016, smaller numbers of migrants continue to use the route to try to reach the European Union, fleeing war and poverty in Africa and the Middle East.
Yet many remain trapped in Serbia for months, unable to enter bordering EU member states such as Hungary and Croatia.
Serbian reception centres currently host more than 3,000 migrants, according to the UN refugee agency in Belgrade.
However, a local NGO, the Centre for the Protection of Asylum Seekers, believes the number is higher.
“This figure is between 5,000 and 6,000 people currently in Serbia,” staffer Rados Djurovic told AFP.