KUALA LUMPUR - Malaysian Prime Minister Najib Razak went shopping in a supermarket on the first day when the country started to implement a 6 per cent consumption tax aimed at plugging a leaky tax-collection system, media reported.

"I noticed that the prices of goods here are reasonable and the essential goods are zero-rated as set by the government," Mr Najib said on Wednesday in a Facebook post, after shopping for some essential items, such as toothpaste and Milo, at the Kota Damansara Giant hypermarket, Bernama reported.

He said on Monday that the goods and services tax (GST) - which does not apply to staple food items such as rice, sugar and cooking oil, as well as some medicines - would not overburden consumers.

"At the same time, we will raise the nation's revenue, and this is for the people's good," he was quoted as saying by Malaysian media.

The government and economists say the GST will help address an inadequate revenue-collection system under which income tax is currently paid by only an estimated 11 per cent of registered companies and 14.8 per cent of employees.

But the GST has prompted demonstrations by opposition parties, who say consumers were being left with the bill for government mismanagement of the economy.