"[Erekat was] ventilated on a high concentration of oxygen and on nitric oxide gas and is in the prone position," a hospital statement said.
"He has received concentrated convalescent plasma with high levels of anti-COVID antibodies. We have consulted with specialists from Tel Aviv, New York and Washington. Prognosis remains very guarded."
Palestinian health minister Mai Alkaila said Erekat had pneumonia after contracting COVID-19 and the hospital said he's in a medically-induced coma.
"Saeb Erekat has been the central figure in Palestinian negotiations with Israel, or in decisions to stay out of such negotiations, for over two decades," Dan Shapiro, former U.S. ambassador to Israel, said.
"Outside of Palestinian Authority President Mahmoud Abbas himself, there is no one who has had such influence on these decisions."
Erekat, 65, was treated for pulmonary fibrosis in 2017 and underwent a lung transplant.