Heavy weapons fire echoed through the capital of Guinea-Bissau Thursday, witnesses said, and soldiers surrounded the residence of former Prime Minister Carlos Gomes Junior, the frontrunner in a presidential election in the small West African state.

The reason for the tumult and Gomes Junior's whereabouts were not immediately known, Reuters reported. Armed soldiers stopped journalists from approaching the residence, which is near the Angolan Embassy in the capital Bissau.

Witnesses said the firing later subsided.

A foreign diplomat told the Associated Press the shooting started after the state radio station signal inexplicably went dead.

I am at the office and I am prevented from leaving, said the diplomat, who could not be named because he was not authorized to speak to the media. The downtown area has been sealed off by the military … I can also tell you that all Guinea-Bissau radio has been taken off the air since 8 p.m. local time and the whereabouts of the prime minister and interim president are unknown.

It was unclear if a coup was in progress. Like in previous military takeovers, the heavy firing is coming after the state broadcaster went silent.

Guinea-Bissau, an impoverished former Portuguese West African colony that has a history of coups and army revolts, is currently in the middle of two rounds of voting to elect a new president to replace Malam Bacai Sanha, who died in a Paris hospital in January after a long illness.

There is some trouble. We don't know what it is. There is shooting, sporadic machine gun fire and there have been three loud bangs ... We hear it is coming from near Carlos Gomes Junior's house, a diplomat in Bissau told Reuters.

State television also stopped broadcasting.

Gomes Junior, who fell just short of an outright majority in last month's first round of the presidential election, is meant to face ex-President Kumba Yala in the run-off on April 29, but Yala and four other candidates have said they will boycott the vote in protest over alleged first-round rigging.

The shooting came just days after news that Angola, which is also a former Portuguese colony but because of its oil resources is much richer than Guinea-Bissau, was ending its military mission to help modernize the army in the smaller state.

Guinea-Bissau has weathered successive coups, attempted coups and a civil war since winning independence from Portugal in 1974. It has been further destabilized by a growing cocaine trade, fueled by traffickers from Latin America who discovered the nation's archipelago of uninhabited islands several years ago. They used the deserted islands to land small, twin-engine planes loaded with drugs, which are then parceled out and carried north for sale in Europe.

The traffickers, according to analysts, have bought off key members of the government and the military, creating what some are now calling a narcostate.

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