A new Croatian centre set up to improve the journey of refugees and migrants opened its doors on Tuesday, receiving about 1,000 arrivals by train on a cold and foggy morning.

The centre was set up over the past two weeks by the Croatian army in a former warehouse on the outskirts of Slavonski Brod, an eastern town by the Bosnian border, and can take in about 5,000 people.

With winter approaching, the centre was established to improve conditions for refugees and migrants, who until now had to walk three kilometres (two miles) in Serbia to reach the border with Croatia, and then often faced a cold and lengthy wait to cross.

Following a deal reached last month between Zagreb and Belgrade, the travellers are now being transferred to the new centre by train directly from the Serbian town of Sid, about 100 kilometres away.

"This will at least decrease their suffering a bit. They will not have to walk and wait in the rain and cold which is especially important for children and sick people," Croatian army spokesman Ivica Orsolic told AFP.

The first 1,000 migrants to arrive at the new centre came from another Croatian camp in the village of Opatovac, near the Serbian border, which was set up when the influx began.

The first train from Sid in Serbia also departed for Slavonski Brod early Tuesday, a spokeswoman for the Serbian minister in charge of refugees told AFP.

As of early evening Monday, the "green" border crossing at Berkasovo, which migrants had earlier been walking across into Croatia, was closed, Croatian police spokeswoman Jelena Bikic said.

Since mid-September, when Hungary closed its border with Serbia to migrants, more than 312,000 people fleeing war and poverty in Middle East, Africa and Asia have transited through Croatia, an EU member with a population of 4.2 million.

Most are heading for Germany or other richer northern European countries, but must travel from Greece through the Balkans to get there.

The new centre consists of several large tents, two of them holding more than 1,400 beds each, and facilities for children, women and sick people. All the accommodation is heated.

"We are prepared... the situation is under control and there should be no problems," Interior Minister Ranko Ostojic said at the weekend.

In recent days, an daily average of about 7,000 migrants have been entering Croatia from Serbia, before being transferred by buses and trains to Croatia's western neighbour, Slovenia.

But the number of migrants surged again on Monday when nearly 9,000 people entered.