Former Malaysian prime minister Mahathir Mohamad yesterday railed against allowing "foreigners" to be given large tracts of land to build property that will be occupied by them, as he took aim at investments from China being brought in by Prime Minister Najib Razak.

Speaking at the launch of his four-month-old opposition party, Tun Dr Mahathir also attacked Datuk Seri Najib for the scandal surrounding state fund 1Malaysia Development Berhad (1MDB), which he said had led to the weakening of enforcement agencies such as the Attorney-General's Chambers and the police.

He said the 1MDB scandal had forced Mr Najib to get foreign investments that would pawn away Malaysian land.

"Singapore was our territory but not now. If we think a little bit, this is happening again.

"Our heritage is being sold, our grandchildren won't have anything in the future," Dr Mahathir told several thousand party members and supporters at an indoor stadium in the Selangor capital of Shah Alam. Top opposition leaders were also present.

Dr Mahathir's speech was streamed live on the website of his Parti Pribumi Bersatu Malaysia, and viewership hit 9,100 at one point.

He did not mention China by name in his hour-long speech.

But he has blogged several times and spoken to the media about his concern that Mr Najib is allowing mainland Chinese companies to buy vast swathes of land, particularly in southern Johor.

Dr Mahathir has also spoken about the possible changes to the country's demography.

When writing last month about Mr Najib's plan for a railway line to link Kuala Lumpur to the east coast states, Dr Mahathir wrote: "They (China) will come with technology and workers from their country.

"The project will last at least seven years, maybe more.

"Their workers, tens of thousands of them, must necessarily be based here, especially in Kelantan, Terengganu and Pahang."

The RM55 billion (S$17.6 billion) East Coast Rail Link is to be financed by China.

In his speech last night, Dr Mahathir, 91, listed several steps that the opposition parties would take if it took power after the next general election, which is widely speculated to be called this year.

Among other things, he said the new government would scrap the unpopular 6 per cent goods and services tax, and would freeze the sales of large assets to foreigners.

Instead of just giving out cash aid like Mr Najib, he said there would be more skills training.

Last night's event was closely watched by both ruling and opposition parties to gauge the organising capability of the new party.

Bersatu was formally approved as a registered political party in September last year.