A nurse who treated Ebola patients in West Africa said she plans to end her voluntary US quarantine and even stepped outside her home briefly.

Kaci Hickox's words and actions signalled a potential showdown with police monitoring her home in Fort Kent, Maine, and state officials seeking to legally enforce the quarantine.

Police stood across the street and watched as Ms Hickox held an impromptu press conference outside with her boyfriend.

State officials are seeking a court order allowing state troopers to detain the nurse, said department of health and human services commissioner Mary Mayhew.

Ms Hickox, who has shown no symptoms of Ebola, told said on television that she was abiding by the state's voluntary quarantine by having no contact with people on Tuesday and yesterday. But she said she will defy the state if the policy is not changed today.

"I remain appalled by these home quarantine policies that have been forced upon me even though I am in perfectly good health," she said.

Her lawyer Norman Siegel said she is not willing to co-operate further unless the state lifts "all or most of the restrictions".

But state officials continued to assert that she should remain in isolation until November 10, the end of the 21-day incubation period for Ebola.

A judge would have to grant the state's request in what could serve as a test as to the legality of state quarantines during the Ebola scare.

Until an order is signed by a judge, state police will monitor Ms Hickox's movement and interactions if she leaves her home, Ms Mayhew said.

Ebola, which is spread through direct contact with the bodily fluids of an infected person, has killed thousands of people in Africa, but only four people have been diagnosed with it in the US.

People cannot be infected just by being near someone who is sick, and people are not contagious unless they are ill, health officials say.

Guidelines recommend monitoring for health care workers like Ms Hickox who have come into contact with Ebola patients. But some states, including Maine, are going above and beyond them.

Ms Hickox, who volunteered in Sierra Leone with Doctors Without Borders, was the first person forced into New Jersey's mandatory quarantine for people arriving at the Newark airport from three West African countries.

She spent the weekend in a tent in New Jersey before travelling to the home of her boyfriend, a nursing student at the University of Maine at Fort Kent.

"I am not going to sit around and be bullied by politicians and forced to stay in my home when I am not a risk to the American public," she said.

Maine Governor Paul LePage, who cancelled campaign events to keep tabs on the situation, commended all health care workers who have volunteered in Africa to treat Ebola patients. But he said the state must be "vigilant" to protect others.

State law allows a judge to grant temporary custody of someone if health officials demonstrate "a clear and immediate public health threat".