Hanoi  - Vietnam's prime minister this week approved an expansion plan in which the capital city of Hanoi will balloon to three times its current size, an official said Tuesday.

The city will swallow the whole of neighboring Ha Tay province and parts of six others, increasing its land area from 920 to 3,325 square kilometers, according to a plan approved by Prime Minister Nguyen Tan Dung on Monday.

"It is necessary to expand the capital city so that it can function better," said To Anh Tuan, director of Hanoi's Architecture and Planning Department. "With its current size, the city can hardly keep pace with development."

The expansion would make the capital city larger than Vietnam's southern economic capital of Ho Chi Minh City, and raise its population from 3.4 million to 6 million people. It would also place urbanized areas of neighboring Ha Tay and Vinh Phuc provinces that have recently attracted substantial foreign direct investment under the control of Hanoi's city administration.

It was not clear what effect the expansion would have on the city's urban planning framework, known as HAIDEP, which was developed in concert with Japan's foreign aid organization, JICA. The HAIDEP plan cost JICA some 7 million dollars.

Japanese urban planner Iwata Shizuo, who directed the HAIDEP plan, said it required areas outside the city's current boundaries for urban needs such as waste disposal and maintaining a greenbelt, but that he had recommended cooperating with adjoining municipalities rather than absorbing them.

"That might have been the start of the discussion of expansion of the urban area from the Hanoi side," Iwata said. " But at that time they didn't mention the expansion would be so huge. I'm a little embarrassed."

Nguyen Thanh Minh, a senior construction ministry official, said the city was still operating based on the HAIDEP plan.

"We won't implement the whole of JICA's programme, but we will use it selectively for the development of the city's urban area," Minh said.

Before taking effect, the expansion plan must be approved by the National Assembly, which is scheduled to consider it on May 13. (dpa)