With British hospitals already struggling to fill their ranks, Brexit could make life even harder for the National Health Service as EU doctors and nurses either stay away or prepare to leave.

The state-run NHS is hugely reliant on EU immigrants to look after aging Britons, and the latest data after the Brexit vote has put the sector on high alert.

“We risk facing a serious staff shortage which will only further worsen pressures on our NHS,” Charlie Massey, head of the General Medical Council (GMC), told a parliamentary committee last month.

Some 60,000 EU nationals work in the NHS, representing about 5 percent of its staff of 1.2 million.

A survey commissioned by Channel 4, published on March 13, showed that 42 percent of them were considering leaving in the next five years, and that 70 percent considered Britain a less appealing place to work in the wake of the referendum.

The number of EU nurses registering to work in the NHS has already plunged by 90 percent since Britain voted to leave the European Union in June, according to figures from the Nursing and Midwifery Council.

Only 101 nurses signed up in December, compared with 1,304 in July, in what Jackie Smith, the council’s chief executive, called “the first sign of a change” after the referendum.

Janet Davies, director of the Royal College of Nursing, the main association of British nurses, told AFP that the national health care system already had 24,000 nursing vacancies and that it “simply could not cope without the contribution from EU nurses.”

British Prime Minister Theresa May has so far refused to grant residency rights to the estimated three million EU citizens living in Britain, saying that this should depend on an agreement on the status of about 1.2 million British nationals in other parts of the union.

“We want guarantees soon,” said Joan Pons, a 41-year-old Spanish nurse working in Gorleston, Norfolk, who has been living in Britain for 17 years.

In Spain, “all the nurses wanted to come here but they are now looking at other countries like France.”

Pons is a campaigner in The3Million movement, an advocacy group set up following the referendum that wants residency rights for EU citizens.

He said the government’s silence on the issue had helped foster a climate of xenophobia.

“I get called all sorts of things on social networks. The other day a Polish nurse told me in tears that a young patient refused to be treated by her because she was foreign,” he said.

The government has vowed a policy of zero tolerance on hate crime incidents, which increased sharply just before and in the immediate aftermath of the referendum.

Pons has three children aged five, 11 and 14 who were all born in Britain, and they are now worried about whether they will need to move to Spain.

“They are scared that we’ll go on holiday and never come back,” he said.

Pons said that if European nurses leave Britain, and British pensioners now living in Spain return home, “the health system will collapse.”

It would certainly add to the health care bill.

Paul MacNaught, director of EU, International and Prevention Programmes at the UK health ministry, has estimated that the presence of 190,000 British pensioners in other EU countries saves the British health system about £350 million (400 million euros, $425 million) per year.

The uncertainty has already proved too much for some EU health care professionals.

“We are thinking of moving to Australia,” a 45-year-old Spanish nurse from Barcelona, who is married to a Spanish doctor, told AFP. She requested anonymity since she has not yet spoken about her plans to her managers.

The nurse has been living in Britain for three years but in recent months, she said, “life has changed.”

She said she now saw only the downsides of living in Britain.

“The bad weather is tiring me out. I didn’t even care before!“