The party of pro-democracy leader Aung San Suu Kyi has won a landslide victory in a historic by-election in Burma.

There have been scenes of celebration after the country’s Election Commission confirmed that the National League for Democracy (NLD) had won 40 out of the 45 open seats.

Addressing the crowds outside NLD headquarters in Rangoon, Aung San Suu Kyi said: "We hope that all other parties that took part in the elections will be in a position to co-operate with us to create a genuinely democratic atmosphere in our nation.”

Ms Suu Kyi, who spent years under house arrest, is now set to enter the 664-seat parliament.

Although she will have very little say in a parliament still dominated by the military and the military-backed ruling party, there is widespread optimism that Sunday’s vote has set Burma on a new course.

Ms Suu Kyi said the result signalled “the beginning of a new era” in Burmese politics after decades under military rule.

Christian Solidarity Worldwide (CSW), which works with persecuted ethnic minority and Christian communities in Burma, gave a cautious welcome to the by-election.

CSW’s East Asia team leader Benedict Rogers said it was a “very significant and “very welcome result” for the country.

“It shows the true feeling of the Burmese people,” he said.

“Their clearly expressed desire is for freedom, justice and democracy, values represented by Aung San Suu Kyi and the NLD whom voters have overwhelmingly supported.

“This is, however, just the beginning and there is still a very long way to go.”

The by-election is the latest in a series of surprising reforms pushed through since President Thein Sein and a partially civilian government came to the helm in 2010.

The European Union’s Trade Commissioner, Karel De Gucht, told the BBC that the by-election result could lead to the EU easing sanctions on Burma.

“Her [Suu Kyi's] party has won the larger part of the seats, that I think is an indication that the elections have been free and fair and that the result reflects the will of the voters," he said.

CSW said the Burmese government must now show its genuine commitment to reform by deepening the process and reforming institutions, legislation and the constitution.

It called for the release of all remaining political prisoners and an end to “severe” human rights abuses in Burma’s ethnic states.

Mr Rogers said the government must initiate a political dialogue with the ethnic nationalities to secure a political agreement and a peace process to end more than six decades of civil war and stop the crimes against humanity being committed by the military.

“Until these steps are taken, the international community should be careful about how it responds to the by-election results,” he said.

“The reforms so far should be recognised, welcomed and encouraged, but pressure should be maintained for more.”

“While some sanctions should be lifted in order to recognise the changes so far, the European Union, the United States, Canada and Australia should not lift all their sanctions in one go, and should ensure that some measures are retained until there is significant further progress, particularly an end to crimes against humanity and war crimes in the ethnic states and a genuine peace process.

“Until all the people of Burma can live in peace and freedom, we cannot say that Burma is free. Today Burma has taken a welcome step forward towards change, but it has not yet changed.”