The ACP-1000 reactors to be supplied by China will be used for the first time, and will produce 1,100MW each, reported the Washington Post.
Costing about $5bn each, the ACP-1000 reactor has been developed on the design of a French reactor built in China in the 1980s.
Pakistan has three nuclear plants. In addition to setting up the new plant in Karachi, the country is planning to double the capacity at Chashma Nuclear Power Plant in northern Punjab province.
However, the new Karachi plant is being opposed in Pakistan due to its location, which is susceptible to tsunamis and threats from Al-Qaeda.
The plant is being planned to be built 20 miles from Karachi, a region populated with about 20 million people.
Washington Post quoted a lawyer Abdul Sattar Pirzada as saying: "You are talking about a city one-third the population of the United Kingdom.
"If there would be an accident, this would cripple Karachi, and if you cripple Karachi, you cripple Pakistan."
According to the news report, China has signed the agreement with Pakistan ignoring an international ban on the transfer of nuclear technology to the country, which has refused to sign the Nuclear Nonproliferation Treaty.
Though China is a member of the Nuclear Suppliers Group, it claims that the promise to support Pakistan’s nuclear plans was made before joining the group in 2004.
A statement from the US embassy said: "China’s expanding civilian nuclear cooperation with Pakistan raises concerns and we urge China to be transparent regarding this cooperation."
