All islanders over the age of 65 and any person with "underlying medical conditions" must self-isolate, the Government of Jersey has announced.
Minister for Health, Deputy Richard Renouf said data showed coronavirus had begun to spread in the island.
From midnight on Thursday, the specified islanders should only leave their homes for a total of two hours per day, under limited circumstances.
Deputy Renouf said the new rules would "shield" the most vulnerable groups.
Ministers announced the first death in Jersey of a patient with coronavirus on Wednesday evening.
Over 65s and those with "less severe" medical conditions should only leave the house:
- To shop for necessities, such as food and medicine
- For daily exercise, including walking, cycling, running, and sea swimming
- Medical reasons
People with medical conditions that put them at "severe risk", including those with cancer, severe respiratory problems, or pregnant women with heart disease, are being asked to "home-isolate".
They should not leave their house for shopping, work, leisure, or travel, the government said.
Jersey's deputy chief medical officer, Dr Ivan Muscat, said these groups were more likely to be hospitalised and were at a greater risk of death if they caught the virus.
The measures were likely to be in place for "a matter of weeks, not days", Deputy Renouf said.
"I must stress to those affected that this is for your own safety, and it requires all of us to ensure that we keep our distance and practice good hygiene, so we don't take the infection into your homes."
The government said it would be mobilising its Community Taskforce to support those having to home-isolate.