New Zealand search officials, who have been called in to assist Fijian authorities, said the inter-island ferry MV Butiraoi was reported missing late Friday.
The 17.5 metre wooden catamaran left from Nonouti Island for Betio Tarawa in the Kiribati Islands on January 18.
The 260 kilometre voyage was expected to take two days.
"We understand the vessel underwent repairs to its propeller shaft just before it departed," New Zealand Rescue Co-Ordination Centre officer John Ashby said.
"The weather in that part of the Pacific is currently moderate with some swells."
A New Zealand Air Force Orion plane has been despatched to conduct an aerial search of the route the vessel was scheduled to take.
Kiribati a nation of 33 atolls and reefs with a total population of about 110,000, lies some 3,460 kilometres (2,150 miles) north east of Fiji.