UK Power Networks, which owns and maintains the power cables in Suffolk, has said on its website a fault was reported this morning at around 4.20am.
Affecting properties in the IP1 6 postcode area it has been caused by a fault with an underground high-voltage cable.
The company estimates 366 of its customers, including at least one school, have been hit by the problem.
It was initially thought power would be restored by around 11am, but this has now been revised to 1.30pm.
A spokesman for the company said: “UK Power Networks engineers are currently on site working to restore electricity to 366 properties in Ipswich, who have been affected by a power cut since 4.21am today.
“A piece of network equipment has developed a fault and needs to be replaced, so we are organising alternative supply routes to restore supplies to homes and businesses affected in the Meredith Road, Kipling Road and Browning Road area.
“We will restore the power as soon as possible, in stages. We realise how difficult it can be to be without power especially in winter months, and apologise for the inconvenience caused.”
Whitton Community Primary School has confirmed it will not open at all today because of the problem.
A message posted on its Twitter account initially said: “School will be closed for the morning as power will not be returned until later. We will open at 1pm, please spread the word.”
However this was later updated to say: “Now not due back on until 1.30. School is freezing so we’re going to stay closed for the day. Sorry everyone, back to normal tomorrow.”
There was also an outage in the IP6 9 area of Suffolk, around Otley, today.
Earlier the spokesman added: “Engineers are on their way to site following a fault on the electricity network system in the Otley area.