MANDALAY, Myanmar - Myanmar’s opposition leader Aung San Suu Kyi fell ill on Saturday as she addressed the largest crowd of her election campaign so far in the second biggest city of Mandalay.

More than 100,000 people gathered to cheer on the tired-looking Nobel Peace Prize laureate as she delivered a speech on the outskirts of the city, but she was forced to take a break saying she did not feel well. NLD sources said the 66-year-old, who is travelling with two personal doctors, had then vomited several times, but she returned to the stage about ten minutes later to continue her address.

“She is feeling better now,” her doctor Tin Myo Win later told AFP, saying Suu Kyi had recently been suffering from a cold. The international icon has had a punishing schedule ahead of by-elections on April 1, campaigning in various parts of the country and meeting a stream of foreign dignitaries in her hometown of Yangon. Her decision to run for a seat, in a constituency near Yangon, is the clearest sign yet of the surprising change taking place in Myanmar since an army-backed government replaced decades of outright military rule last year.

“I came to Mandalay to ask for help,” she told the crowds, asking the people to vote for her National League for Democracy (NLD) party in the by-elections, which will see her stand for parliament for the first time. “I haven’t seen such a big audience since 1988,” she said, referring to the year she swept to prominence as Myanmar’s leading pro-democracy campaigner, before being put under house arrest by the junta. “We have overcome many difficulties by resisting, with the people’s support, for more than 20 years. We will continue like this. Please believe in us.”

Although the opposition cannot threaten the ruling party’s majority, even if it takes all 48 seats up for grabs in April, the by-election is seen as a key test of the new regime’s commitment to reform.

“Our future road will be really tough and difficult. Democracy is not easy to get and also not easy to strengthen straight away,” Suu Kyi told the Mandalay gathering.

Suu Kyi’s NLD party won a landslide victory in an election in 1990 while she was under house arrest, but the ruling junta never allowed the party to take power and she spent much of the next two decades in detention.

The next election in 2010 swept the army’s political allies to power but was marred by widespread complaints of cheating and by the absence of Suu Kyi, who was again under house arrest and released a few days later.

The regime has since welcomed the NLD back into mainstream politics as part of its reforms, which have also included the release of hundreds of other political prisoners and the signing of ceasefire deals with ethnic rebel groups.

Western countries have begun to ease sanctions on Myanmar in response to the recent promising steps and they are expected to further relax restrictions if April’s polls are free and fair.

In a speech by videolink to Canada this week, Suu Kyi thanked countries that maintain sanctions on Myanmar, saying they were aiding its transition to democracy and urging supporters of reform to remain vigilant.

Last week she hit the campaign trail in the northernmost state of Kachin, where she appealed for unity among the country’s disparate ethnic groups and called for an immediate end to conflict between the regime and Kachin rebels.