Melbourne has posted its hottest day on record for the first half of September after warm, windy conditions swept across Victoria.

Wind gusts of up to 85 kilometres an hour have been recorded so far, but the gusts could reach as much as 100 kilometres on Saturday night.

Senior forecaster Richard Carlyon says northerly winds have fuelled the hot weather across the state.

"We got to 29.9 in Melbourne, we have never had a day above 29 degrees in the first half of September," he said.

"It wasn't an all-time September record - that was 31.7 degrees back in the late `80s.

"This is unprecedented.

"But there is a cold front pushing in from the west and that will bring some milder air across the state overnight.

"The temperature is not expected to be nearly as high on Sunday," he said.