The dead in Balochistan included 80 people whose bodies were recovered after a dam burst late on Thursday. The remainder came from six other districts inundated by around 10 days of heavy rain.
"We have confirmed reports that 250 people have died in Balochistan due to floods," the provincial chief minister's media consultant, Raziq Bugti, told AFP.
More than 2,000 people were missing, while 40,000 had lost their homes in Lasbella, Gwadar, Khuzdar, Awaran, Ketch and Panjgoor districts, Bugti said.
The air force, navy and army have mounted a massive operation in Balochistan to rescue survivors and provide shelter, medical aid, drinking water and food. Paramilitary troops, police and private relief organisations are also taking part.
The World Health Organisation warned of possible disease dangers.
"Over the next few days we may see the emergence of serious health problems among the population in the affected areas," its country director for Pakistan Khalif Bile said in a statement.
Infectious and waterborne diseases could spread rapidly, he warned. Crisis management cell officials told AFP another seven people were killed and more than a dozen were missing after the small Gaggo dam burst in neighbouring Lasbella district late on Saturday, leaving about 100 people homeless.
Four more people died in Babarshore village in Pasni district due to heavy rains, a senior official at Balochistan's crisis management cell said.
Heavy rains also breached two small dams, one in the coastal town of Gwadar and one in Ketch. Mud villages were damaged but no one was hurt, he said.
While Pakistan's south was battered by rain, its north was suffering from heavy snowfalls.
Around 40 people were feared dead after two avalanches late on Saturday in the mountainous region of Abbottabad, police said.
"About 35 people are feared dead in Dubair village of Kohistan district where four houses had been buried under snow and rocks," Abbottabad police chief Amin Hashim told AFP.
Bad weather had prevented rescue teams reaching the site but they would keep trying, Hashim said.
Another avalanche hit a home in nearby Phool Kot and buried eight people, he said. Two had been dug out alive, three bodies were recovered and three people were missing under the snow and rubble.
OUR MUZAFFARABAD CORRESPONDENT ADDS: The death toll from avalanches in the Neelum valley rose to 54, officials said on Sunday.
"Thirty-one dead bodies have been recovered till Sunday evening as the death toll in Mayyatan Wali Seri hamlet in worst snow-hit upper Neelum valley area has risen from 33 to 41," legislative assembly member from Neelum valley Mufti Mansoorur Rehman said. "Death toll will increase ultimately as many areas of the valley remained completely cut off," he said, adding that relief goods, medicine and rescue workers could not reach the spot as snow was falling continuously till Sunday afternoon in the area.
"We were trying to reach the spot with medicines, doctors and relief goods with the help of an helicopter but could not succeed due to bad weather," he said.
Meanwhile, army airlifted dead bodies of two soldiers to Muzaffarabad from Leepa valley who were killed while burying under a snow avalanche.
They were identified as Muhammad Banaras, resident of Bhimber, and Muhammad Fayyaz, resident of Peerian Bandi Chanari.
Their dead bodies were dispatched to their homes after funeral prayers. Officials feared that death toll may rise as there was no communication link with remote areas of the Neelum valley.