Zimbabwe's President Robert Mugabe has been detained by the country's military, who have seized control of the national broadcaster, ZBC.
Soldiers and army vehicles are on the streets of the capital, Harare, where gunfire and artillery were heard on Wednesday.
Is it a coup? The military insists not - but it certainly has a lot of the hallmarks.
The signs that a coup is under way have always been the same across the world and across the decades. Here are the key things to watch out for when a takeover is on the cards.
1. Nobody ever says it's a coup
Firstly, be aware that almost nobody mounting a coup ever says that's what they're doing.
Zimbabwe's envoy to South Africa, Isaac Moyo, explicitly said there was no coup as the government was "intact" with no "military takeover".
"We are only targeting criminals around [President Mugabe] who are... causing social and economic suffering," Mr Moyo said on state TV. "As soon as we have accomplished our mission, we expect that the situation will return to normalcy."
The "situation" probably looks more alarming to those on the wrong side of the military action, however.
This kind of semantic wriggling is common in attempted coups.
In restive Venezuela, which has seen violent anti-government protests since the spring, military officers launched an unsuccessful uprising against President Nicolas Maduro in August.
"This is not a coup but a civil and military action to re-establish constitutional order," said the group's leader, Juan Caguaripano.
Venezuela's ruling Socialist Party disagreed, and deputy leader Diosdado Cabello branded it a "terrorist attack" on Twitter.
2. Where's the head of state?
When checking for a likely coup, look at where the head of state is. President Mugabe is being held in Harare under house arrest, according to the office of South Africa's President Jacob Zuma. He reportedly said in a phone call that he was fine.
There is no confirmation of the fate of his powerful wife, 52-year-old Grace Mugabe, who has been vying to be her husband's successor. However, an MP from the opposition Movement for Democratic Change, Eddie Cross, told the BBC she had fled Zimbabwe for Namibia on Tuesday night.
Detaining the target of the uprising is a vital stage in proceedings. As the BBC's diplomatic correspondent Jonathan Marcus observes, the failure of Turkey's attempted coup in July 2016 stemmed from the plotters' inability to immobilise President Recep Tayyip Erdogan.
Foreign embassies can become a place of refuge for ousted or imperilled leaders. When President George Bush Senior invaded Panama in 1989, repressive strongman General Manuel Noriega holed himself up in the Vatican's embassy in Panama City.
And sometimes, the head of state will show up in an entirely different country. In Honduras in 2009, troops deposed President Manuel Zelaya and forced him onto a plane. When he arrived in Costa Rica, he said he had been kidnapped in his pyjamas.
Almost three months later he made a surprise return - and installed himself in Honduras's Brazilian embassy.
3. People (and gunfire) on the streets
Waves of popular protest are a key coup signifier. Protesters will often call for a return to democracy and the fall of a repressive regime, only for the military to move in and take power.
In Egypt, President Hosni Mubarak was forced out by mass protests during the Arab Spring of 2010-11, which also swept across Libya, Tunisia, Yemen and Syria. The turning point came when the Egyptian army announced that it would not use force against the demonstrating crowds. Mr Mubarak stood down, and a military administration stepped into the breach.
As Turkey's failed coup unfolded in July 2016, civilians actually took to the streets in support of the threatened president. When bridges over the Bosphorus strait in Istanbul were blocked by renegade troops, the public joined pro-Erdogan soldiers to confront them.
There has been a lack of public protest in Zimbabwe, where tensions were triggered by Mr Mugabe sacking his political deputy, Emmerson Mnangagwa, in favour of his wife, Grace. The streets are said to be calm, but armoured military vehicles are patrolling the capital.
4. Foreign powers warn their nationals
Even if not sheltering an endangered leader, embassies on the ground have a duty to keep their nationals safe, so they'll start offering guidance.
In Zimbabwe, the UK Foreign Office has advised Britons "currently in Harare to remain safely at home or in their accommodation until the situation becomes clearer".
The US embassy tweeted that it would be closed on Wednesday "due to ongoing uncertainty".
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5. State media seized
Getting the message out is important, so rebels often try to seize state or private media to use as their mouthpiece.
In Zimbabwe, the military has successfully overrun the headquarters of the state TV station, ZBC.
Taking to the airwaves is no guarantee of success, however.
In Turkey in 2016, the doomed army faction used a state broadcaster to claim it had seized power to protect democracy from President Recep Tayyip Erdogan. In fact, the revolt was suppressed.
Zambia in 1997 saw an even less successful effort, with an attempted coup that lasted just three hours. At six o'clock one morning, a man calling himself Captain Solo announced on state radio that he had taken over the country, that the heads of the army and police were dismissed, and that President Frederick Chiluba had until nine to surrender or be killed. The president swiftly went on air to say six people had been arrested, and thanked his troops for "a job well done".
6. Borders, bridges and airports close
To impose control over a country - or even just its capital city - it helps to close the borders, and seal bridges and other infrastructure that allow people in and out.
In September 2015, presidential guards who led a coup in Burkina Faso ordered the sealing of land and air borders, as well as a night-time curfew.
Perhaps the most striking lesson in airport control comes from Pakistan in 1999, when Prime Minister Nawaz Sharif tried to sack powerful army chief General Pervez Musharraf, and a battle for supremacy began.
Gen Musharraf was in Sri Lanka when he got word that Mr Sharif planned to move against him, and made an airborne dash from Colombo airport to Karachi. Air traffic control refused permission for the plane and its 200 passengers to land, and the pilot was ordered to divert it, first to Oman, then to India.
The general ordered the pilot to keep circling Karachi, even though fuel was running dangerously low. The plane was only brought down safely when pro-Musharraf soldiers surrounded the airport's control tower. The general was whisked to safety, and claimed control of Pakistan hours later.