The worst of the weather is likely to hit Christchurch between 6pm today and 3am tomorrow.

Ex-tropical Cyclone Gita is curving towards the country after it left a devastating trail of destruction through Tonga and parts of Samoa, southern Fiji and New Caledonia.

Forecasts are suggesting Christchurch could get more than 70mm of rain in 24 hours, which is enough to flood streets.

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Even higher rainfall is expected in Banks Peninsula, where strong wind gusts of 70km/h or greater are expected. This, combined with the heavy rain heightens the risk of slips and trees falling.

High tide on Tuesday night is due about 9pm and will coincide with the heavy rain, increasing the risk of flooding, which may be as bad as last July's storm.

Air New Zealand is now warning of "major disruptions" as Gita hits tomorrow, when wind gusts are predicted to top 120km/h.

The effects of the cyclone could be intensified or lessened depending on which way the storm tracks once it hits the West Coast.

Civil Defence response teams will head out late this afternoon door-knocking people.

At this stage it is unclear what impact the wind will have on the off-shore wave current and whether there will be an associated storm surge.

People living in areas prone to flooding should lift valuable possessions off low-lying floors and to park their cars on higher ground.

People are also advised to secure, or move inside, anything that could cause damage in strong winds.

The Christchurch City Council has temporary pumps ready and contractors are going around the city checking the stormwater network and stopbanks to ensure they are functioning as they should.

City council contractors may not be able to get to every stormwater grate in the city so residents are asked to check grates outside their property to ensure they are clear of leaves and other debris.

The council will also be checking the city's water supply wellheads before, during and after the storm and isolating any that are vulnerable to flooding.

People needing to access healthcare in the Canterbury DHB area should attend outpatient and other scheduled, hospital-based appointments as they normally would - providing it's safe to go out and the roads are clear, a spokeswoman for the DHB said.

If people need to access unplanned non-urgent care, they are advised to call their usual GP number first for advice 24/7 and to check that they are open.

Communities in Takamatua, Duvauchelle and Akaroa who rely on stream-fed water are being asked to limit their water use during the storm as the streams are likely to become too dirty to use.

Contractors will be on standby to close roads and respond to any flooding issues until the cyclone has passed. Some roads that frequently flood may be closed as a precaution if it appears they are likely to flood.

Civil Defence are closely monitoring the storm and will consider whether it is necessary to activate an Emergency Operations Centre once it becomes clearer which way the storm is tracking.

People should avoid non-essential travel during the height of the storm. Anyone who must travel should check the NZTA website for up-to-date information on State Highway closures and travel advice.

People should not drive through floodwaters.

People are also asked to delay washing the dishes or laundry tomorrow when the wastewater system will be under pressure from rainwater infiltration.

Kerbside rubbish collections will continue as normal this week, although the city council says people should make sure bin lids are closed flat to avoid them blowing open and rubbish being spread around the neighbourhood.

The city council says bins should not be put out overnight, but on Wednesday morning.