Tropical Cyclone Ruby has brought heavy rain to New Caledonia as it's moving along its east coast.

The storm is forecast to drop up to 250 mm of rain.

The cyclone's centre, with gusts of 170 kilometres an hour, is expected to reach the southern end of the main island by tonight.

Forecasters say there are heavy swells of up to eight metres.

In the north, which has been on full alert since yesterday, thousands of people have lost power.

Ruby is expected to lie about 65 kilometres northeast of Noumea this evening.

Strong to gale force winds on the periphery of the system are also expected about the southern islands of Vanuatu from this evening.

On Wednesday Ruby is expected to move southeast away from the Pacific Islands, but forecasters say, says despite its current trajectory, the cyclone doesn't pose a major threat to New Zealand.