More than 1,000 students and staff members at two US universities have been quarantined or sent home in a bid to stop a measles outbreak.

Cases of measles in the US have reached a 25-year high, sparking sweeping efforts by authorities to contain the virus.

The University of California and California State University – both in Los Angeles – ordered the precautions after it was discovered two people infected with measles had visited their campuses.

About 325 of those affected were cleared to return by Friday afternoon, having proved their immunity to the infection through either medical records or tests.

Those under quarantine were told to stay at home and avoid contact with others, and were barred from taking public transport.

Anyone who must travel for an emergency should notify public health officials first.

The county’s public health director, Dr Barbara Ferrer, said the measures were legally binding and anyone violating them could be prosecuted.

“Measles actually kills people, so we have to take that really seriously,” said Dr Armand Dorian, chief medical officer at USC Verdugo Hills Hospital.

The number of measles cases in the US is at its highest for a quarter of a century, climbing to nearly 700 this year.

Many have blamed the surge on parents refusing to vaccinate their children because of misinformation about the supposed dangers.

California State University reported it had placed 875 people under quarantine this week, while the University of California said 129 students and faculty were quarantined.

Those affected were believed to have been possibly exposed to either an infected UCLA student who attended classes in two buildings earlier this month, or a person who visited a library on the California State University campus.

Officials said the quarantine would end at UCLA on Tuesday and at California State University on Thursday.

Earlier this week, President Donald Trump urged everyone to get vaccinated, while authorities across the country have attempted to crack down on exemptions to vaccinating children.

The Centres for Disease Control and Prevention recommends that everyone over a year old should get the vaccine, unless they already contracted measles as children.

The virus usually causes a fever, runny nose and rash but a small number of cases can lead to deadly complications. (AP)

Update news