Former Prime Minister Benjamin Netanyahu, who succeeded his arch rival Mr Sharon as leader of the right-wing Likud party last month, was among the first to offer his wishes for a full recovery.
"Like the entire people of Israel, I also pray for the well being of Prime Minister Ariel Sharon," Mr Netanyahu said in a statement.
His wishes were echoed by President Moshe Katsav who said that "along with all the Israeli people I pray for the well being of the prime minister and wish him a speedy recovery."
The leader of the secular Shinui party, Tommy Lapid, also issued his best wishes for the Prime Minister and hoped he would make a quick recovery.
"The whole nation, his friends, opponents and everyone else, is worried and wishes him all the best and a quick recovery," Mr Lapid told the Channel 2 television network.
"It is a dramatic night and I hope it won't end over-dramatically. I hope that the system will cope with the situation in a manner befitting a progressive nation."
Bush concerned
US President George W Bush said that he and the first lady shared "the concerns of the Israeli people about Prime Minister Ariel Sharon's health" and were praying for his recovery.
"Prime Minister Sharon is a man of courage and peace," the president in a brief statement.
"On behalf of all Americans, we send our best wishes and hopes to the Prime Minister and his family."
US Secretary of State Condoleezza Rice said she had learned from the Israeli government that Mr Sharon was receiving the medical attention that he needed.
"Our thoughts and prayers are with Prime Minister Sharon, his family, and the Israeli people," Ms Rice said.
"We wish the Prime Minister a full recovery."