Malawian President Bingu wa Mutharika is in a critical condition in hospital after suffering a heart attack, a minister and officials in the southern African country have said.

The Reuters news agency reported chaotic scenes as the 78-year-old leader's wife, Calista, and senior cabinet ministers left a hospital in the capital Lilongwe, where Mutharika had been admitted after collapsing on Thursday morning.

"There was panic," one hospital staff member, speaking on condition of anonymity, told Reuters. "We have never been prepared for such an eventuality. He suffered a cardiac arrest and the condition is still unstable."

A minister, speaking to Reuters on condition of anonymity, said Mutharika's condition was "very critical".

State media confirmed that Mutharika had been admitted to hospital, but did not say what ailment he was suffering from or what his condition was. It said he would be flown to South Africa for emergency treatment, although it did not say when he would travel.

Joyce Banda, the country's vice president, wished Mutharika a quick recovery, local media reported.

The relationship between the president and Banda has been rocky since the vice president was kicked out of the ruling Democratic Progressive Party in 2010.

She was ejected from the party after a row over succession. According to the Malawian constitution, she is first in line to take over in the case of the death of the head of state.

Such a situation would appear to put her on a collision with Mutharika's inner circle, including Peter Mutharika, the country's foreign minister and the president's brother.

Mutharika has deputised in Bingu's absence in the past.

Police on Thursday were deployed across the country's capital, while 15 army officers took up positions around Banda's residence, witnesses said.

UK row

Mutharika, a former World Bank economist, came to power in 2004 and presided over a seven-year economic boom, underpinned by foreign aid and some favourable rains, that made Malawi one of one of the world's fastest-growing countries.

Economic growth, however, came to a halt last year, after a dispute with the United Kingdom led to diplomatic expulsions in both countries and the freezing of millions of dollars in aid to Malawi.

The aid suspension led to an acute shortage of dollars in the Malawian economy, hampering fuel, food and medicine imports.

Mutharika's diplomatic isolation and economic plight worsened in July 2011 when the US shelved a $350m programme to overhaul the country's dilapidated power grid, after police killed at least 19 people in a crackdown on an unprecedented wave of anti-government protests.