Vanuatu appears to have come through Cyclone Ula relatively unscathed.

Heavy rain and strong winds have battered the country overnight, in many of the same areas hit hard by Cyclone Pam last year.

The tropical cyclone system was upgraded to category four last night and is currently passing near Vanuatu's southern fringe.

The cyclone has been described on Facebook as not "making things too miserable" for residents.

World Vision spokesperson Chloe Morrison said aerial inspections will be carried out this morning to assess the extent of the damage.

"We're expecting to see minimal damage and that hopefully will just be that there will be some rain damage, potentially some low lying areas of flooding."

Morrison confirmed there's concern the latest rain may have damaged crops farmers planted since Cyclone Pam.

"Low rainfall has meant that [farmers] have been failing, and strong rain that came through with Cyclone Ula could have caused further agricultural damage - Assessments today and aerial flyovers will establish the extent of that."

Chloe Morrison said because some islands are very remote, it's hard to know the extent of damage.

A Fiji Meteorological Service spokesman says the cyclone is picking up speed and weakening in intensity as it heads south.

Strong winds and heavy rain are expected in southern regions.

A cyclone alert is also in effect for the New Caledonian island of Mare.

The cyclone is expected to pass close to islands in the Tafea Province later this afternoon.