Palestinian medics said two of the wounded were in a critical condition. Three of those hit were elderly farmers, a hospital source said, but the identity of the other four was not immediately clear.
The Israeli army said they shot at people who had approached the fence that separates Gaza from Israel in an area where Palestinian militants had previously planted bombs targeting their patrols.
"Initial investigation of the incident suggests that tank shells were fired against the terrorists," a military spokesman said.
It was the first time the Israelis have fired into Gaza since four days of heavy fighting in March, which left 25 Palestinians dead, mainly gunmen.