The police said recent raids are aimed at "curbing illegal migration" following a deadly clash between migrants in the Hungarian border last week.
Police in Serbia arrested seven people on suspicion of smuggling people from Serbia to Hungary as part of a days-long crackdown on irregular migration, the local police said on Friday.
The extensive probe comes in the wake of a shooting that occurred last week in the border area, killing three migrants and wounding one.
The arrests were made both in the capital Belgrade and in Subotica, a city near the border with Hungary.
Since the shooting last Saturday near the border town of Horgos, police have launched daily raids in the forested area.
Thousands of people have been camping in the area, looking for ways to cross with the help of people smugglers, the local police said in a statement.
A total of 738 migrants were found, some near the border with Hungary, but others in a town near the border with Bulgaria in the east, the statement added.
When found, migrants are usually transferred to reception centres throughout the country. Migrants pay €2350 each to cross the border according to various reports.
Reports of violence and gun battles have become common near the border between Serbia and Hungary, a European Union member state.
Hundreds of Serbian officers were dispatched Saturday into a border area with Hungary after the recent shootings.
Interior Minister Bratislav Gasic, who visited the area, pledged that "we will not move from here until every person responsible for any criminal act or incident is removed.”
Serbia lies at the heart of the so-called Balkan land route of migration toward Western Europe, which leads from Turkey to Greece and Bulgaria, and then on to North Macedonia, Serbia or Bosnia.
Crossings along the Balkan land route usually intensify in the fall as bad weather prevents migrants from taking the perilous journey over the Mediterranean Sea.
Hungary’s staunchly anti-immigrant government has put up a razor-wire fence on the borders with Serbia to stop the influx and has pushed back into Serbia migrants who enter Hungary.
People smuggling gangs, however, have multiplied in the border area, often clashing for control.
President Aleksandar Vucic said last week that Serbia could bring in the military “to fix this,” state RTS television reported.