Munich federal police chief Hubert Steiger told reporters in Munich that the southern border between Freilassing and Lindau would be under the heaviest controls.
Under normal circumstances, there are no border checks on people moving between countries that are party to the Schengen Agreement, which covers most of mainland Europe.
But the rules of the pact allow states to declare temporary exceptions to the rule.
Police hope to prevent a repeat of anti-capitalist demonstrations in Frankfurt in March, which drew large numbers of violent protesters from outside Germany, especially Italy.
But their colleagues in northern Germany will also be keeping an eye out for demonstrators travelling by road from Scandinavia.
“Today we're in the set-up phase. Officers are moving through the deployment area and are beginning to use the infrastructure we've built,” Steiger said.
Meanwhile, the town of Garmisch-Partenkirchen refused permission for anti-G7 demonstrators to set up a tented camp on a nearby field.
Authorities in the mountain resort town said that the field was in danger of flooding and camping there would endanger participants.
The “Stop G7 Elmau” group had already said that they would take legal action if their plan wasn't allowed to go ahead.