Two cases of measles in Fiji's capital could lead to the virus spreading in some of the most densely-populated areas, the World Health Organisation says.
There have now been 14 cases of measles confirmed in Fiji, including two in Suva.
Fiji's government said the latest case was a man,36, from the Serua/Namosi subdivision, where a total of 12 cases had been confirmed.
Health official Sunil Chandra said the government was taking precautions to avoid a larger outbreak in the capital.
There are more than 175,000 people living in Suva, including the outer suburbs.
The measles vaccine is currently in limited supply and is only being administered to priority groups; residents of the Serua/Namosi, children aged between six months and three years, and people travelling overseas.
The restrictions would change after new vaccine stock arrived later this week, the government said.
WHO official Jose Hagan said Fijian authorities needed to focus on vaccinating priority groups in Suva, which might have been missed.
"So, this puts additional pressure on the government to identify populations in Suva that might be particularly or maybe less likely to be vaccinated than the general population...
"Cases in a dense population are a challenge but I think Fiji knows what to do and WHO is working with them on that."