Liberia and Sierra Leone have declared states of emergency, ordering the closure of schools and markets and the quarantining of affected communities, in an attempt to halt the Ebola epidemic that has claimed more than 700 lives across three west African nations.

The leaders of both countries have cancelled planned trips to Washington for a US-Africa summit next week so they can meet on Friday in Conakry, the capital of Guinea, to discuss the crisis.

They will be joined by the leader of the Ivory Coast, which has porous frontiers with Liberia. Remote border officials say they've recently begun turning away people fleeing from affected communities. The World Health Organisation has also launched a $100m special fund to tackle the outbreak.

In Nigeria, where a Liberian civil servant died of Ebola after flying to the commercial hub of Lagos, airport authorities began screening passengers for high temperatures who were arriving from places at risk.

Liberia's president, Ellen Johnson Sirleaf, announced the emergency measures after a closed-door meeting earlier this week in which medical officials painted a stark picture, according to an aide present at the meeting.

Internal ministry of health reports obtained by the Guardian show health workers saw 606 people suspected of having the extremely contagious virus in a single day this week.

In Bomi county, one of the areas recommended for quarantine, the report noted "both probable and negative cases are being held in the same room with no attention". Health officials there were requesting training, it added.

"It's a dire situation. The spread is overwhelming health workers and facilities. We need all the help and support we can get from the international community," said Lewis Brown, Liberia's information minister. He said communities hit hardest would be quarantined for as long as necessary by security forces. "It's an emergency, so we hope people will understand."

Sierra Leone's president, Ernest Bai Koroma, said the state of emergency would last between 60 and 90 days. House-to-house searches to trace victims will be conducted and new at-risk neighbourhoods will be placed under quarantine if necessary.

A nationwide hunt was sparked in the capital, Freetown, when a patient was forcibly removed from hospital last week. She was reported to have died while being returned to the facility in an ambulance two days later.

The latest action comes as senior western officials, including from the US and UK, held meetings to assess the risk of Ebola reaching their shores. The US has recalled its Peace Corps volunteers from the region.

The measures taken are similar to those that rapidly ended a 1997 Ebola breakout in Uganda, which has sent in a medical team to help.

Many rural communities view Ebola with much the same fear and misunderstanding as westerners did when the Aids epidemic began, and have sometimes attacked overstretched health officials struggling to contain the epidemic. Those on the frontlines have been among the hardest hit by the disease, which has claimed the lives of Liberia and Sierra Leone's most experienced Ebola doctors.

There are signs that some public awareness campaigns are yielding results. Doctors were forced to turn patients away at one of Liberia's main Ebola isolation wards in a sign many were belatedly coming forward. Some residents in the capital, Monrovia, initially protested against a new ward being set up, fearing it would endanger them.

Sylvia Johnson, a Monrovia resident, pulled her grandson out of summer school at the beginning of the week after seeing a government poster of graphic corpses of Ebola victims. "He cried, but no child will control me. It will be better for him to live and attend many more vacation schools than get sick from Ebola," she said.

Spread by contact with bodily fluids of infected patients, bush meat or surfaces, this Ebola outbreak has killed 729 people since it originated in Guinea, where health officials took several weeks to pinpoint the source to a remote village in the country's forest hinterlands. By then, it had spread to Sierra Leone and Liberia.

Nigerian authorities have mobilised unusually swiftly, underlying concern about an outbreak in the continent's most populous nation and major commerce hub. Officials began printing information leaflets, including in widely-spoken pidgin English.

Akintayo Ugwani, a businessman, said: "It's terrifying. I have to get on a flight every couple of days and each time now I'm just wondering, am I entering a flying coffin?"

The country's main airline, Arik Air, has suspended flights between Nigeria, Liberia and Sierra Leone, while international airports and seaports have been placed on red alert, with passengers being monitored. Ghana also began screening passengers.

Philip Hammond, the British foreign secretary, chaired an emergency Cobra meeting amid warnings that the virus could be a threat to Britain, although health experts said the country was well prepared to deal with any potential cases.

Hammond said no British national had been affected by the outbreak and there had been no cases in the UK.

The UK announced a £2m package of assistance to the International Federation of the Red Cross (IFRC) and Médecins sans Frontières, which are tackling Ebola in Sierra Leone and Liberia. The European commission said it would allocate an additional €2m (£1.6m) – on top of €1.9m – to help contain the spread of the epidemic.

"The level of contamination on the ground is extremely worrying and we need to scale up our action before many more lives are lost," said Kristalina Georgieva, EU commissioner for humanitarian aid.

Wade Williams in Monrovia contributed to this report