At least six fatalities, including five children, have been linked to the outbreak, which has also hit other island states such as Tonga and Fiji.
Samoa has reported more than 700 cases across all areas of the country, prompting the government on Friday to invoke emergency powers.
Declaring a state of emergency, the government said plans for compulsory measles, mumps and rubella (MMR) immunisations would be published on Monday.
“MMR vaccinations for members of the public who have not yet received a vaccination injection is now a mandatory legal requirement for all of Samoa,” it said.
A national emergency operations centre to coordinate the measles response was opened on Monday.
However, no information was immediately available on how the vaccinations would be administered or whether those who were not immunised would face sanctions.
Children are the most vulnerable to measles, which typically causes a rash and fever but can also lead to blindness, brain damage and death.
Samoa has closed all schools, kindergartens and the country’s only university in a bid to halt the virus’ spread.
New Zealand, which is experiencing its own measles outbreak in the Auckland region, will this week send 12 nurses and 3,000 MMR doses to assist Samoa’s public health response.
University of Auckland immunologist Helen Petousis-Harris said even though measles was already widespread, the mass rollout of vaccinations could help limit the number of cases and reduce the death toll.
She said it was also important to boost Samoa’s low levels of immunisation and help prevent future outbreaks.
“In Samoa, the proportion of people who are immune to measles is very, very low, one of the lowest in the world,” she told AFP.
“So if they aren’t able to improve that, this is going to happen again.”
The country’s vaccination programme was briefly suspended last year when two babies died shortly after being given the MMR vaccine.
Subsequent investigations found the problem was not the widely-used vaccine but the fact that the nurses administering prepared it incorrectly.
Neighbouring Tonga last week announced government primary schools and kindergartens would be closed until later this month as the number of measles cases in the kingdom approaches 200.
Fiji has reported four cases but says they are contained to a township west of the capital Suva.