Monsoon floods in Pakistan have killed 371 people and affected nearly 4.5 million, the government's disaster relief agency said on Friday.

Pakistan has suffered devastating floods in the past two years, including the worst in its history in 2010, when catastrophic inundations across the country killed almost 1,800 people and affected 21 million.

As in 2010 and 2011, most of those hit by the latest floods are in Sindh province, where the National Disaster Management Authority (NDMA) said 2.8 million were affected, with nearly 890,000 in Punjab and 700,000 in Baluchistan.

Nearly 290,000 people around the country have been forced to seek shelter in relief camps, NDMA said in figures published on its website.

The floods began in early September, with nearly 80 killed in flash floods, mostly in the northwest and Pakistan-administered Kashmir.

An NDMA spokesman said the government was not yet appealing for foreign assistance.

"The government's point of view is that the situation will be handled from own resources," Ahmad Kamal told AFP.

More than a million acres (400,000 hectares) of crops have been destroyed by the floods across the country, NDMA said, and nearly 8,000 cattle have been killed.

UN children's agency UNICEF, quoting a separate flood assessment, said at least 2.8 million people had been affected, including 1.4 million children, of whom more than 390,000 are under five.

UNICEF said it was providing 183,000 people a day with drinking water but warned it urgently needed more funds.

"Children from very poor families are among the worst affected by the severe flooding and they need our immediate help," said UNICEF Pakistan Deputy Representative Karen Allen.

"UNICEF urgently needs $15.4 million to scale up its water, sanitation and hygiene response to reach around 400,000 people over the next three to six months."

UNICEF said that according to its assessment, more than half of those affected by the floods were concentrated in just five districts, two each in Sindh and Baluchistan and one in Punjab.

It said 360,000 people had been left without shelter and three quarters of children in the five worst-affected districts were unable to go to school, either because the buildings have been destroyed or because they are being used as temporary shelters.

The UN agency voiced particular concern about children forced from their homes, saying loss of access to safe water supplies left them vulnerable to diseases such as diarrhoea, malaria, measles, polio and pneumonia.

More than 20,000 families in Sindh have been provided with hygiene kits including water purification tablets, UNICEF said, as part of efforts to prevent deadly water-borne diseases.