It's a hot night at the Sakifo festival, in a beachside park on the island of La Réunion the French overseas department in the Indian Ocean. The Spanish/French star Manu Chao was an earlier headliner, and now it's the turn of a remarkable and controversial local singer. Christine Salemcomes on shaking a kayamb, a tray-like percussion instrument constructed from cane stalks. Backed only by two other percussionists, one of them sitting astride a large roulé drum, she delivers an extraordinary and compelling set that switches from the deep and soulful, with echoes of Nina Simone, through to furious, hypnotic chanting and throaty growls.

Only a generation ago, the police would have smashed her instruments, and Salem would have been arrested for singing in this way, because she was daring to sing maloya, the banned, African-influenced music of the Creole descendants of the slaves who worked the island's sugar plantations. With its mixture of thunderous percussion and improvised call-and-response vocals, it's the Indian Ocean answer to the blues. The Catholic church disapproved of it because it was used in the servis kabaré ceremonies, in which the drumming and chanting cause participants to enter a trance-like state in which they say they come face-to-face with their ancestors. The authorities disliked it because of its links to slave culture, and were concerned that it was also being used in a secular form by a political party campaigning for greater autonomy or independence from France.

The ban on maloya was lifted in 1981, but when Salem sings today it's easy to see why the Catholic church disapproved. "They thought the trance music was the devil's song ... but it's great music," she says.

Salem draws her inspiration from maloya's religious forms. One of her strongest songs, Djinn, is a haunting, powerful piece that comes out of her own experience at trance ceremonies. Performing it live, she breaks away from the slinky rhythms of earlier numbers for a section of frenzied percussion and howling vocals that develop into a furious bluesy chant in which the Creole lyrics tell of meetings with her ancestors. Her remarkable performance is a reminder of the divisions on the island. Réunion is popular with tourists from France and elsewhere, but behind the beach hotels and restaurants, there still exists a Creole culture that links back to the slavery days.

Salem was born 41 years ago in a poor district of Saint-Denis, the island's administrative capital, where her mother worked as a cleaner and cook. She never met her father, "but I heard he played accordion", nor did she study music at school, but she remembers as a child hearing the maloya band Ziskakan playing in Saint-Denis. "They were very different from the way they are now," she says. "Far more traditional. They made a big impression on me, although I didn't come from a musical family." She wrote her first song, "a blues, in English, about love" aged 12, and later joined different groups playing sega, the Indian Ocean dance style, in the tourist hotels, "just for the experience, and because I loved singing".

She was in her early 20s when she attended – just as an observer – her first servis kabaré ceremony, and she was soon drawn into the trance ceremonies and their music and began to study the special songs used for each different stage of the process.

Although maloya was predominantly sung by men, she started singing it with her own group in the late 90s. "It wasn't forbidden for women to sing it, but even now people find it strange to hear a lady singing it. When people first heard me they thought a man was singing because I have such a deep voice. They were surprised when they saw me," she says with a smile.

Salem believes passionately that maloya deserves a wider audience, and she has travelled to Madagascar, the Comoros and Zanzibar, researching the roots of the form, and experimenting in modernising it, not least by working with the American-French folk-blues band Moriarty, who added bass and guitar to some of her songs. But she mostly performs with the traditional percussive lineup that is still used in the trance ceremonies. "But I don't use quite the same music on stage, in respect for the ancestors, and because if we did that, my audience might go into a trance!"

She believes that her experiences at the ceremonies when she was younger brought her in contact with her own ancestors. "When you go into a trance for the first time, you ask the ancestor where he is from, and after that you recognise who is there." So you know where your ancestors come from? "Yes, I know exactly. They are mostly from Africa, from Mozambique and around there. So that's where I am going to do my research next."

But at the same time she continues to promote her singing career; she has already performed in Australia this year and she is tipped to be one of the highlights at Womad next weekend.Salem may be bringing maloya to a new global audience, but her modernising approach has caused unease to some traditionalists, not least the island's greatest veteran exponent of the style, Firmin Viry. On the Sunday morning of the Sakifo festival there's a free concert down by the fishing port of Terre Saint, a showcase for the male heroes of maloya, headlined by Viry. Now in his late 70s, he sings enthusiastically for the most of the morning, spurred on by up to 10 percussionists and support from Danyel Waro, who himself made a memorable appearance at WOMAD two years ago.

Afterwards, Viry sat by the sea and talked of the days back in the 70s when he had to sing secretly, in defiance of the French authorities. He was, he says, "very lucky" not to have been discovered and sent to jail like other musicians. A supporter of the Communist party, for him, maloya was protest music, and he wrote about "love, life and employment". So how does he regard Salem and her very different approach? "She is invoking the spirits of the dead, and the way I was brought up, what you do in the house you don't do outside," he says. "The religious side should be kept at home and not performed on stage, and her songs are about the ancestors, not politics. It's a very dangerous approach because we are a mixed people in Réunion, and some words can disturb the spirits."

There is certainly a sense of urgency and danger in Christine Salem's performance, and that's part of her appeal. She deserves to become maloya's first international female celebrity – as is her intention. "It's important for me, because it used to be forbidden. It's a challenge."