With players sweltering in 36 Celsius (96.8 Fahrenheit) temperatures, the tournament's five-part heat stress scale hit five.
The scale measures four climate factors -- radiant heat (strength of the sun), air temperature in the shade, relative humidity and wind speed.
The lowest level reading is one and the highest five, at which point play is suspended and the roofs are closed on its three main stadiums -- Rod Laver Arena, Margaret Court Arena and John Cain Arena.
Organisers said conditions had improved and play was resumed at 5pm (0600 GMT).
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