By Marko Djurica

HORGOS, Serbia (Reuters) - About 150 migrants, mainly from Afghanistan and Pakistan, on Monday started a hunger strike in a field in Serbia on the border with Hungary to demand passage to the European Union.

The group, which initially numbered about 300 people, had traveled to the border over the weekend from Belgrade and settled in a field about 100 m (yards) from Hungary's wire-fenced frontier with Serbia.

Last month Hungary limited the number of daily entries to a maximum of 30, creating a bottleneck in Serbia. It also allowed police send back illegal migrants detained within eight km (five miles) of its border with Serbia.

The migrants on hunger strike, wearing red baseball hats, told Reuters they had traveled by train and on foot. Some said they have already been deported back to Serbia.

They said they would refuse food until Hungary opens the border.

"The food is (brought) here, but nobody wants to eat it. The border stays closed so we will sit here, they should open the border," said Abdul Malek, an Afghan in his 40s.

Aleksandar Vulin, Serbia's minister for social affairs, said authorities would prevent any unrest. Migrants said they will protest peacefully.

"We secured them accommodation and all their needs, but we will not tolerate anything that would evolve into endangering of public order," Vulin said on Monday while visiting a refugee camp in the area.

According Serbia's commissariat for refugees, about 3,000 migrants remained stranded in the country, including 800 awaiting entry into the EU in camps at the Horgos and Kelebija border crossings with Hungary.

Vulin said migrants deported from Hungary to Serbia must now apply for asylum or face expulsion.

(Reporting by Aleksandar Vasovic; Editing by Angus MacSwan)