Authorities in Pakistan say they are mobilising to receive as many as half a million people newly displaced by fighting in and around the Swat Valley.
Pakistan's military is fighting "for the survival of the country" against Taleban militants in the Swat valley, the prime minister says.
A minister in North West Frontier Province told the BBC that officials were trying to deal with one of the world's "huge" internal displacements.
Yusuf Raza Gilani was speaking as the army tried to retake Swat's main town, Mingora, where a curfew is in force.
Pakistan's president has promised all-out war against militants in the area.
The government signed a peace agreement with the Swat Taleban in February, allowing Sharia law there, which was heavily criticised by Washington.
The army said its "full-scale" assault had killed more than 170 militants in 24 hours, with the loss of 10 troops.
The militants then moved towards the capital, Islamabad.
It accused the Taleban of trying to stop civilians leaving the area.
With Pakistani jets and helicopters pounding the Swat Valley and neighbouring districts, the UN says the area threatens to become the scene of one of the world's biggest displacement crises.
The government signed a peace agreement with the Swat Taleban in February, allowing Sharia law to be locally imposed.
Up to 15,000 troops have been deployed to take on 4-5,000 militants.
But emboldened Taleban forces advanced beyond Swat towards the capital, Islamabad, and the strategy came under increasing fire from Washington.
Pakistani forces have been waging an air and ground campaign
'Complex situation'
The army said it had killed 55 more militants on Saturday, having said that more than 140 militants had died in earlier clashes.
The Pakistani offensive against militants has already displaced some 200,000 people, while a further 300,000 are estimated to be on the move or about to flee, the UN says.
The fighting has already displaced some 200,000 people, while a further 300,000 are estimated to be on the move or about to flee, the UN says.
Sitara Imran, minister for social welfare in North West Frontier Province, called the exodus "one of the huge displacements, internal displacements in the world".
Sitara Imran, minister for social welfare in North West Frontier Province, called the exodus "one of the huge displacements, internal displacements in the world".
"We are preparing ourselves with the help of the federal government, we asked international donors," she told the BBC's Newshour programme.
'Feeling helpless'
She said all her department's doctors and social welfare staff had been mobilised and that holidays had been suspended as they worked to prepare for the influx.
"This is not a normal war," Prime Minister Gilani told reporters on Saturday, Reuters news agency reports, "this is a guerrilla war."
"The whole Swat [population] is coming out from [the Swat Valley] so, naturally, it is a very difficult and complex situation," she said.
"This is our own war. This is war for the survival of the country," he said.
The BBC's Barbara Plett reports from a refugee registration centre in the area that some people left behind almost everything they owned, so fearful for their lives they did not even take time to lock the door.
The BBC's Mark Dummett in Islamabad says that for the first time since the military launched the offensive against the Taleban in the Swat valley, the fighting has spread into the centre of Mingora.
Despite now-abandoned attempts to secure a peace deal in and around Swat, the area - close to the border with Afghanistan - has long been riven by tensions.
An indefinite curfew is preventing people from fleeing the area.
Some 550,000 people had already been displaced by fighting in other parts of the border area since August - before the current crisis - the UN refugee agency said.
"We are feeling so helpless, we want to go but can't," Mingora resident Sallahudin Khan told Reuters news agency.
"We tried to leave yesterday after authorities relaxed the curfew for a few hours, but we couldn't as the main road leading out of Mingora was literally jammed with the flood of fleeing people."
The army has also accused the Taleban of holding the civilian population hostage and blocking their exit.
Mobile phone networks, water and electricity have all been cut in the town which is normally home to half a million people. There are fears that food and medicine will run out if the fighting does not end soon.
Our correspondent says the government is hoping for a quick victory, while it still has the support of the Pakistani people.
The US says the militants in northern Pakistan pose a direct threat to its security, and has demanded they be confronted.
The US says the militants in northern Pakistan pose a direct threat to its security, and has demanded they be confronted.
In an interview during a visit to Washington, President Asif Ali Zardari confirmed on Friday that Pakistan wanted to "eliminate" the militants it is fighting.
Pakistani military spokesman Gen Athar Abbas said the military's objective was to eliminate the militants from the Swat valley and also the neighbouring districts of Dir and Buner.
"This is an offensive - this is war," he told PBS television. "If they kill our soldiers, then we do the same."
Militant strongholds were hit from the air on Friday as troops conducted operations on the ground.
Pakistani forces have been waging an air and ground campaign
Pakistani military spokesman Gen Athar Abbas said troops had killed 143 rebels in Swat, 25 in Lower Dir and six in Buner, losing seven soldiers in Swat and three in Lower Dir.
Militants were "on the run and trying to block the exodus of civilians from the area", he said.
Earlier, he told the BBC the military's objective was to eliminate some 4-5,000 militants from the Swat Valley and neighbouring districts of Dir and Buner.
The Pakistani military says it is trying to help displaced civilians by establishing camps where they can seek shelter.
But reports suggest many thousands of civilians under threat from the fighting are unwilling or unable to move.
Roads have been blocked or reportedly mined by the rebels.
The Pakistani military has also imposed an indefinite curfew over swathes of the region.
A local journalist in Mingora told the BBC that electricity and water had been shut down and markets had been closed since Thursday. There was, the journalist said, a real threat of food shortages in the coming days.
While the army accuses the Taleban of holding the people left in the Swat Valley hostage, those who have escaped blame both sides for the conflict and the dire position of the civilians caught between them, correspondents say.
