Rafael Grossi, who visited the plant for several hours, also said he would continue to worry until the situation at Zaporizhzhia had stabilised. Both Russia and Ukraine say they fear a possible radiation disaster as a result of shelling that the two sides blame on each other.
"We are not going anywhere. The IAEA is now there, it is at the plant and it is not moving - it's going to stay there," Grossi told reporters.
"We're going to have a continued presence there at the plant with some of my experts."
Those experts, he said, would provide what he called an impartial neutral technically sound assessment of what was happening on the ground.
"I worried, I worry and I will continue to be worried about the plant until we have a situation which is more stable, which is more predictable," he said.
Local residents presented Grossi with a petition and documentation of damage caused by shelling in the area.
Ukraine and Russia accuse each other of creating a risk of atomic catastrophe by shelling the plant, where the situation has been unravelling in recent weeks.