Albert Barnes Commentary Numbers 11:1

"And the people were as murmurers, [speaking] evil in the ears of Jehovah: and when Jehovah heard it, his anger was kindled; and the fire of Jehovah burnt among them, and devoured in the uttermost part of the camp." — Numbers 11:1 (ASV)

See the marginal rendering. They murmured against the privations of the march.

The fire of the Lord — Probably lightning; compare Psalms 78:21.

In the uttermost parts — Rather, in the end. The fire did not reach far into the camp. It was quickly quenched at the intercession of Moses.