Nine people have needed medical care after eating the Riviera Farms baby spinach from Costco.

Health authorities say their symptoms have also included delirium, spiked heart rates and blurred vision.

Riviera Farms says it believes the spinach was contaminated by a weed, but no other products have been affected.

New South Wales Health has warned any packets of the brand's spinach with an expiry date of December 16 are not safe to consume and should be thrown out.

It also urged anyone who has experienced any unusual symptoms after eating the spinach to immediately seek hospital care.

"No one has died, so we're very happy with that and we hope it remains that way, but these people are quite sick... to the point of marked hallucinations, where they are seeing things that aren't there," Dr Darren Roberts, from the state's Poisons Information Centre, told the Sydney Morning Herald.

A Riviera Farms spokesperson said they had taken action immediately, asking shops to remove them from shelves.

"There is no suggestion, and to our knowledge no possibility, that any other products have been impacted by this weed," they said.

All of those affected so far are from Sydney, NSW Health said, but it has alerted authorities in other states as it investigates.