Pro-democracy leader Aung San Suu Kyi has suspended her campaign a week before Myanmar's by-elections after falling ill, her party says.

Kyi Toe, a spokesman for her National League for Democracy party, said Suu Kyi's personal physician had advised her to rest after she fell ill with vomiting during a campaign tour to the Mergui archipelago in the south.

But Suu Kyi 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 party, according to an photographer from the AFP news agency.

"I'm trying to keep in good health," she told the crowd, apologising for making only a brief speech before rushing to catch a flight back to Yangon. "I have been encouraged by the people," she said.

Tin Myo Win, her doctor, said her ill health was due to exhaustion and hot weather and that her blood pressure was low.

The Nobel laureate was vomiting and was put on an intravenous drip after her boat got stuck on a sandbank for several hours on Saturday during a trip to the town of Myeik, according to the doctor.

Released from house arrest in 2010, the 66 year old has travelled thousands of kilometres around the country for her party. She herself is running in a constituency south of Yangon.

Kyi Toe said Suu Kyi's campaigning had been suspended at least through Tuesday.

Test for reforms

Myanmar's April 1 polls will see Suu Kyi stand for a seat in parliament for the first time, and are viewed as a key test of the government's commitment to reforms.

Myanmar was ruled by the military for decades until elections last year brought a nominally civilian government to power - albeit one with close links to the army.

Suu Kyi and her party have accused the government of taking measures to hamper her party's campaign, such as selective bans on using large public venues including football stadiums. They have also said the voting registries contain the names of dead people, opening up the potential for electoral fraud.

The upcoming polls are the first in which the Suu Kyi's party is taking part since it won a 1990 general election - only to have the army refuse to let it take power.

The opposition boycotted the 2010 general election, claiming it was neither free nor fair, leaving the field open for a landslide victory by the army-backed Union Solidarity And Development Party and the installation of Thein Sein - the former junta's prime minister - as president.

Thein Sein initiated reforms, including the release of political prisoners, and the NLD agreed to rejoin electoral politics after election laws were changed to meet its objections.