(AFP) - Sustained gunfire was heard on Tuesday near the seat of government in the coup-prone West African state of Guinea-Bissau, AFP reporters said, as a regional bloc condemned what it called an "attempted coup".

Heavily-armed men surrounded the Palace of Government, where President Umaro Sissoco Embalo and Prime Minister Nuno Gomes Nabiam were believed to have gone to attend a cabinet meeting.

The building is located on the edge of the capital Bissau, close to the airport.

People were seen fleeing the area, the local markets were closed and banks shut their doors, while military vehicles laden with troops drove through the streets.

The former Portuguese colony is an impoverished coastal state of around two million people lying south of Senegal.

It has seen four military putsches since gaining independence in 1974, most recently in 2012.

In 2014, the country vowed to return to constitutional government, but it has enjoyed little stability since then and the armed forces wield substantial clout.

A 36-year-old Frenchwoman living in Bissau, Kadeejah Diop, said she had rushed to pick up her two children from school and witnessed armed troops entering the Palace of Government.

"They made all the female workers leave. There was huge panic," she told AFP by phone from her home. "Right now, we are holed up indoors. We have no news."

Reacting to events, the Economic Community of West African States (ECOWAS) issued a statement saying it "condemns this attempted coup" and urged soldiers to "return to their barracks".

The bloc warned that it "holds the military responsible for the wellbeing of President Umaro Sissoco Embalo and members of his government."

The United Nations said Secretary General Antonio Guterres was "deeply concerned with the news of heavy fighting in Bissau."

He called for "an immediate end to the fighting and for full respect of the country’s democratic institutions," the UN's statement said.

- Election turmoil -

Embalo, a 49-year-old reserve brigadier general and former prime minister, took office in February 2020 after winning a second-round runoff election that followed four years of political infighting under the country's semi-presidential system.

He was a candidate for a party called Madem, comprised of rebels from the African Party for the Independence of Guinea and Cape Verde (PAIGC) which had led Guinea-Bissau to independence.

His chief opponent, PAIGC candidate Domingos Simoes Pereira, bitterly contested the result but Embalo declared himself president without waiting for the outcome of his petition to the Supreme Court.

Late last year, the armed forces chief said members of the military had been preparing to launch a coup while the president was on a working trip to Brazil.

Troops had been offering bribes to other soldiers "in order to subvert the established constitutional order", armed forces head General Biague Na Ntam said on October 14.

The government spokesman denied his account the following day.

In addition to volatility, Guinea-Bissau struggles with a reputation for corruption and drug smuggling.

Its porous coastline and cultural ties have made it an important stop on the Africa trafficking route. In 2019, nearly two tonnes of cocaine were seized.

Three countries in West Africa -- Mali, Guinea and Burkina Faso -- have experienced military takeovers in less than 18 months.

The region's mounting instability is due to discussed on Thursday at an ECOWAS summit in Accra, Ghana.

© Agence France-Presse