A woman has gone on a racist rant against two shoppers at a Coles supermarket in Melbourne's west, threatening them with a food tin and abusing staff as they tried to defuse the aggressive situation.

An account of the rant suggests the woman became aggressive when she thought two women of African appearance had pushed in front of her at the checkout at Coles in the Woodgrove Shopping Centre in Melton on Wednesday afternoon.

"I was here, I was here first," the woman yells in the video.

As staff attempt to take her to another register she picks up what looks like a Milo tin and threatens to throw it at one of the two women.