More than half a million households and businesses in northern Malaysia will be without water for up to four days from Wednesday due to engineering works at a major treatment plant, officials said.

The disruption has forced hundreds of manufacturers in Penang state -- often dubbed the "Silicon Valley of the East" -- to suspend operations.

Most schools have closed and some hospitals have postponed minor surgeries.

About 100 water tanks have been deployed to help ease the situation, but some residents expressed anger over the disruption.

"Four days without running water is absurd," Ooi Chin Hock, a former investment banker who filled up six large plastic containers to stockpile water at his home, told AFP.

"(This is) a black dot on the state," he added.

Technicians carrying out the repair works at the Sungai Dua water treatment plant, which supplies water to about 80 percent of the state, were replacing two huge leaking and rusted water valves.

Leaky pipes in other locations would also be replaced during the four-day interruption.

"Work is progressing as planned," Penang Water Supply Corporation chief executive K. Pathmanathan told reporters.

Pathmanathan said they hoped for a gradual resumption of water supply from Thursday.

Lee Teong Li of the Federation of Malaysian Manufacturers in Penang said most of its members would close for the first two days and hope for some partial water supply resumption after that.

"We will run into millions of dollars in losses. We will lose revenue, since we have to pay for workers while being shut down," he told AFP.

Penang counts manufacturing and tourism as key economic sectors. It is home to global electronic firms like Intel, AMD, Hewlett Packard, Motorola, Clarion and Flextronics.