Edward Kennedy in hospital after 'stroke'

She added that he is undergoing tests at Massachusetts General Hospital to determine the cause of the seizure.

“Senator Kennedy is resting comfortably, and it is unlikely we will know anything more for the next 48 hours,” she said.

Mr Kennedy went to Cape Cod Hospital this morning “after feeling ill at his home”, Ms Cutter said. After discussion with his doctors in Boston, he was then taken to Massachusetts General.

An official who declined to be identified by name, citing the sensitivity of events, earlier said that Mr Kennedy had stroke-like symptoms. The hospital declined to comment on his condition.

Hyannis Fire Lieutenant Bill Rex told The Associated Press that an emergency call came in from the Kennedy family compound at 8.19am (12.19pm Irish Time). A man was transported to Cape Cod Hospital and then transferred by air at 10.10am (2.10Irish Time) from Barnstable Municipal Airport to Massachusetts General.

David Reilly, a spokesman for Cape Cod Hospital, said Mr Kennedy was taken to the hospital at about 9am (1pm Irish Time) and stayed for about an hour before being flown by helicopter to the Boston hospital.

Senator John Kerry, of Massachusetts, did not speak to reporters when he arrived at the hospital shortly after 1pm.

Mr Kennedy, 76, has been in the Senate since election in 1962, filling out the term won by his brother, John F Kennedy.

In October, he had surgery to repair a nearly complete blockage in a major neck artery. The discovery was made during a routine examination of a decades-old back injury.

The hour-long procedure on his left carotid artery – a main supplier of blood to the face and brain – was performed at Massachusetts General. This type of operation is performed on more than 180,000 people a year in the US to prevent a stroke.

The doctor who operated on Mr Kennedy said at the time that surgery is reserved for those with more than 70% blockage, and Mr Kennedy had “a very high-grade blockage”.

Mr Kennedy is the lone surviving son of the famed political family. His eldest brother, Joseph, was killed in a Second World War II plane crash. President John Kennedy was assassinated in 1963 and his brother Robert was assassinated in 1968.

Democratic presidential candidate Barack Obama, beginning a tour of hospitals in Eugene, Oregon, told reporters that he had been in touch with the senator’s family.

“Ted Kennedy is a giant in American political history. He’s done more for healthcare than just about anybody in history. We are going to be rooting for him. I insist on being optimistic about how it’s going to turn out.”

Mr Kennedy gave Mr Obama’s presidential campaign a big boost this year with his endorsement and has campaigned actively for the Illinois senator.

Arizona Senator John McCain, the likely Republican presidential nominee, said he awaited word on Mr Kennedy’s condition.

“Senator Kennedy’s role in the US Senate cannot be overstated. He is a legendary lawmaker, and I have the highest respect for him. When we have worked together, he has been a skilful, fair and generous partner.”

Mr Kennedy was preparing to host the annual Best Buddies Challenge event this afternoon, a fundraiser for the Best Buddies organisation founded by Anthony Kennedy Shriver which helps people with learning difficulties.

Hundreds were expected to participate in the event, which started with a 100-mile (160km) bicycle ride from the Kennedy Library in Boston to Hyannisport, and ended with a concert at the Kennedy compound.

A man walking near the hospital was startled by the news when he asked about the reason for the large media presence.

“Ted? Is he all right? Jeez, I’m taken aback. I just saw him on television yesterday,” said Jerry Leonard, 76, a retired bartender.

“He’s a Kennedy. His name is synonymous with this area. I’m a Bostonian, too, and he’s done a lot for us around here and for the senior citizens in particular. I don’t know him but I feel a connection.”