According to police in Burgenland, the wave of migrants arriving across the border left police scrambling to arrange transport to reception centres.
"We will wait and see what the situation is in the next few hours and tonight, if more people come. This is absolutely possible," police spokesman Helmut Marban said.
Police believe that a regional train stopped on the Hungarian side of the border, allowing the group of several hundred to disembark and begin their journey to Austria on foot.
Austria has reinstated border checks and vehicle inspections to intercept people smugglers, but continues to assist asylum seekers to make their way to Germany, or to claim asylum in Austria if they prefer.