Melbourne has sweltered through its hottest April 1 on record – and that's no April Fool's Day joke.

It was a case of "April sun in Melbourne" rather than Cuba, with the temperature in the CBD hitting a maximum 33.4 degrees at 3.06pm on Tuesday, toppling the existing record 33.2 degrees on April 1, 1941.

It was the hottest start to April since records began 1856 and the warmest April day in nine years.

Bureau of Meteorology senior forecaster Terry Ryan said it was not an April Fool's Day joke because "you can't do them after midday".

He said it was Melbourne's equal ninth-hottest April day and the hottest April day since April 10, 2005, when it was 34.5 degrees.