Pakistani authorities have breached a strategic dyke in flood-affected Punjab to ease pressure on flood defences downstream and protect urban areas.
More than 700,000 villagers have been forced to flee their homes.
Much of the water is reaching Pakistan from Indian-administered Kashmir where flood levels are now falling.
There have been chaotic scenes at one of the region's main airports, Srinagar, as tourists and migrant workers struggle to leave.
The death toll in the two countries has passed 450, with troops deployed to rescue people and provide assistance.
The flooding is the worst Indian-administered Kashmir has seen in decades. Officials say 400,000 people are stranded there and at least 200 people have died.
Pakistan has not experienced floods as devastating since 2010 - officials say 254 people have died in the past few days.