Emergency authorities are warning of high fire danger this weekend with searing temperatures expected to set a record on Saturday night.

The temperature is set to peak at 41 degrees on Saturday. It is forecast to drop down to 28 degrees in the evening, which would make it the hottest December night in Melbourne since records began.

The Bureau of Meteorology has forecast a high of 37 degrees for Friday with a weak cool change expected in the evening. The mercury hit 37.2 degrees on Thursday.

A cool change is expected for Sunday about midday.