The lockdown applies to almost everyone, except essential services. Private vehicles are also banned on the roads from 7am until 5pm.
People without the measles vaccine have been told to leave a red flag or cloth outside their homes.
In the first day of the shutdown, it's estimated about 6000 vaccinations were administered.
On Monday, Samoa expanded the eligibility of the vaccination programme, which has been made mandatory under local law.
Measles vaccinations are now available for people aged six months to 60 years.
Meanwhile, 70 Hawaiian medical experts are in Samoa to assist with its mass measles vaccination campaign.
A team of 55 nurses and 15 physicians arrived in Apia yesterday and will take part in a door-to-door screening effort.
Hawai'i's Lieutenant Governor has applauded the Samoan government's moves to boost the country's vaccination coverage, saying it is saving lives.
Josh Green, who is leading the team from Hawai'i, said he had witnessed the toll of the outbreak firsthand but was hopeful of an end in sight.
"Many hundreds or thousands more were immunised or saved...because of the bold action you've taken.
"But there is going to continue, I would presume, to be some fatalities, less and less I would expect, because you have done such a good job of getting people immunised so quickly."
Two experts from the US Centers of Disease Control have also arrived in Samoa.
The CDC's Robert Linkins said it was also sending several people to Fiji to coordinate a regional effort.
"We're also very concerned about the neighbouring islands...that are also at risk of importation of measles and are actually already seeing some cases.
"So, we're worried about the potential threat that they're facing."
-RNZ
