Ill health has forced Aung San Suu Kyi to abruptly cancel further campaign travel, her party said on Sunday, just a week before Myanmar by-elections that are seen as a key test of political reforms.

The Nobel laureate, who is running for a seat in parliament in the April 1 polls, was put on a drip and ordered to rest by her personal doctor after falling ill in the town of Myeik in the far south of Myanmar.

But she pressed ahead with a final rally in the remote area on Sunday and was cheered by tens of thousands of people as she urged supporters to vote for her National League for Democracy party, according to an AFP photographer at the scene.

"I'm trying to keep in good health," she told the crowd, apologizing for making only a brief speech before rushing to catch a flight back to Yangon.

"I have been encouraged by the people," she said.

NLD deputy information officer Kyi Toe said Suu Kyi's health had "deteriorated" during the trip.

"According to the advice of her family doctor Tin Myo Win, she will take a rest at home. She should not travel far for trips anymore," he told AFP.

A statement from the NLD confirmed the decision to cancel a final campaign trip on Tuesday and Wednesday to Magway, the central Myanmar region where her father was born.

An increasingly tired-looking Suu Kyi has fallen ill once before during her grueling schedule of rallies and speeches across the country.

Suu Kyi fell ill on Saturday after the boat she was traveling in got stuck on a sandbank for several hours during her trip, Tin Myo Win said earlier on Sunday.

"She is exhausted because of being on the boat for such a long time," he said, adding that she had low blood pressure and had been vomiting.

Next week's polls are the first time Suu Kyi, whose Kawhmu constituency is near Yangon, has been able to stand for election.

The NLD cannot threaten the ruling party's majority even with a strong result in the April vote.

On Wednesday, Myanmar said it had invited US, European and other observers for the vote. President Thein Sein also vowed to ensure the by-elections were "transparent" in talks with Cambodian Prime Minister Hun Sen, according to a Cambodian government spokesman.