The level of testing for contamination in frozen veges has been slammed by a leading advocate for food standards.

Green Party MP Sue Kedgely is alarmed such products that are commercially processed, packaged and labelled overseas are granted unconditional entry into New Zealand by MAF Biosecurity.

She wants more testing and compulsary country-of-origin labelling on all imported frozen veges.

"We have one of the most woefully inadequate testing-at-the-border procedures in the world, which is completely undermining the consumer," Kedgley said.

"So little testing is done on these sorts of foods that we can't have any confidence in the safety of our imports.

"It's a joke, and the potential for serious contamination has always worried me.

"Basically, they're treating New Zealanders as guinea pigs and it's totally unsatisfactory."

You could be forgiven for thinking your frozen veges are homegrown, particularly because the latest figures from Statistics New Zealand show we exported more than $420 million of vegetables in 2008.

But a supermarket visit reveals many come from China - untested and without labels to identify their country of origin.

Tests in Australia in 2005 revealed that imported frozen vegetables contained high levels of the potentially deadly E. coli bacteria.

Baby corn and other vegetables from China had up to 240 E. coli microbials per gram - there is no "acceptable" level.

Australian current affairs show Today Tonight exposed Chinese farms using untreated animal and human waste from nearby toilet blocks as fertiliser, before exporting their produce.

The New Zealand Food Safety Authority did not consider conducting similar tests on New Zealand imports after the revelations, saying they had no reason to suspect imports were unsafe.

Gary Bowering, of the New Zealand Food Safety Authority, said all fresh produce, no matter where it was grown, had the potential to carry illness-causing bacteria.

"These products have been residue tested from time to time in some of our ongoing monitoring [and] there have been no results of concern."

During our trip to the supermarket, we picked five packets of frozen veges.

McCain Carrot, Cauliflower, Broccoli and Sugar Snap Peas mix, and Woolworths Select Broccoli Florets are labelled "Product of China".

Packages of Pam's Asian Stir Fry Mix, Signature Range Thai Stir Fry and Wattie's Stir Fry are labelled as being packed in New Zealand from "local and imported ingredients".

A Progressive Enterprises spokesman, Bill Moore, said the company, which owns the Woolworths, Foodtown and Countdown chains, took great care when choosing suppliers for its Select and Signature Range products.

"Imported products are frequently subject to more intensive testing procedures than products that are domestically sourced," Moore said.

"Products are tested on a regular basis to ensure the quality standards remain high."

McCain Foods marketing director for Australia and New Zealand, David Boyle, said the company imported less than 2 per cent of its vegetables from China.

"We have established an extensive testing regime for all our vegetable imports from suppliers in China," Boyle said.

"We are conscious of the need to test all products as food safety is of paramount importance to our company."

Pam's and Wattie's did not return calls.

Consumer New Zealand research manager Belinda Allan said the organisation was not worried about the safety of imported frozen vegetables, but wanted clearer and mandatory country of origin labelling.

"That would be our only concern; that people are not able to make that informed choice," she said.

"However, I do think we have to have a certain amount of faith that the food has met New Zealand standards, because there are very thorough tests that are done.

"There is a lack of information for consumers about where their food has come from."