The federal government is optimistic blackouts can be avoided, even as millions of Australians in five states face forecast potential power shortfalls within hours.

Households and businesses in New South Wales and in Queensland’s south-east and coastal areas were again asked to conserve electricity on Tuesday, amid warnings of potential blackouts from 5-9pm.

Queensland is expected to be short of power from 4.30pm until midnight and NSW from 5pm to midnight.

Potential power interruptions are also forecast for Tasmania and South Australia between 6.30 and 7.30pm.