Prime Minister John Key says he is concerned that New Zealanders could become "tenants in their own land" and that is why the Government is looking at overseas investment rules around land sales to foreigners.

A TV3 poll released tonight showed 75.5 per cent of voters want the rules tightened, with only 8 per cent saying they should be relaxed.

Finance Minister Bill English is reviewing the Overseas Investment Act and Mr Key said at his post-cabinet press conference today he didn't want to prejudge the result of that.

He said it was necessary for the processes to be rapid and efficient, because foreign investment was welcome when it created job opportunities.

"We're also having a look at the broader issue of land because of the concerns that we hear in the community," he said.

"I am concerned about the risk that New Zealanders become tenants in their own land."

Mr Key said the fact that the big Crafar farms were on the market, with a Chinese bidder, had brought the issue of land sales into sharp focus.

He didn't think public concern related to the fact that one of the bidders was Chinese.

"I don't think it's specific to is because of the scale of the investment," he said.

"My view is it wouldn't make much difference if it was any other international buyer looking to buy that sizeable block of property."

Mr Key said his own concern was about the trend he was seeing.

"There's no question that New Zealand is a great place to produce food," he said.

"We know there's international concern about food security and we know there is a real demand to potentially buy up New Zealand farmland.

"I just think if we are going to allow that to happen on a wholesale basis, we should do that with our eyes open...we should be aware of what that means and that's why I've asked the minister to have a look at it."

Mr Key agreed that farm debt was affecting the situation because it was one of the reasons farms were going on the market.

"There has been too much debt on some farms and in some areas farmers have been losing money for some time," he said.

"Sheep and beef has been very tough for some people recently and in terms of dairy farms, even those that have a high payout are struggling under large amounts of debt."

The TV3 poll questioned 1000 voters and had a margin of error of plus or minus 3.1 per cent.