Head of maintenance at Caulfield Grammar School Alex Taylor said he saw smoke over the park about midday.

"The wind was blowing away from the school so there was no threat to us ... We were pretty fortunate I think.

"Because it is school holidays, the year 12s are in trial exams, we were on standby and monitoring it but luckily we didn't have to evacuate."

The school backs onto the eastern side of Jells Park and Mr Taylor said he could see red helicopters circling the area.

"It's got a lake there so they're probably picking up water from there," he said.

By early Thursday afternoon, fire crews were yet to contain large fires in the south-east and north-west corners of the lake area and smaller fires in other areas.

Mr Taylor said the smoke had mostly disappeared by 2pm and a cool breeze was blowing in as the temperature dropped.

Authorities released smoke and emergency vehicles warnings for the area.

Temperatures in Melbourne soared above 29 degrees at the time the fire was reported in what has been the city's warmest day since April 20.