Dozens of workers at a FIFO mining camp in Western Australia's Pilbara region have been struck by a major gastro outbreak.

The WA Country Heath Service has confirmed 20 people have gone to the Karratha Health Campus with gastroenteritis symptoms over the past two days.

Owners of the Searipple Village workers' camp in Karratha said 26 people were affected by the outbreak, but CFMEU north-west organiser Paul Ferreira said he believed the total number of affected workers could be as high as 60.

It is understood the WA Department of Health is investigating.

A spokesperson for Searipple Village, which is owned by Fleetwood, said "extra cleaning of common surfaces" had started and antibacterial gel and spray had been provided in the village.

"The staff and management of Searipple wish these guests a speedy recovery from their illness and apologise for the discomfort and inconvenience experienced," Searipple Village said in a statement.

Searipple said it was fully cooperating with a review by the Department of Health and City of Karratha to determine the source of the outbreak, and would also review its food preparation and handling standards.

"The village has been in operation for 10 years, and has not experienced a large outbreak of gastrointestinal symptoms prior to this week."

Searipple Village is a camp for fly-in fly-out workers at Karratha in WA's Pilbara region. ( ABC North West WA: Sonia Feng )

The ABC has been contacted by several people who said they had continuously complained about conditions at the camp for months and nothing had been done.

One said there had been raw sewage overflows reported to Searipple management almost monthly over the past year, but it is believed state and local government authorities only became aware of the recent raw sewage flow 10 days ago.

A spokesperson for Searipple Village said a drain had recently been blocked, causing sewage issues, and had since been cleared.

Other complaints include concerns about food handling, overflowing bins and excrement from feral cats at the entrances to buildings.

A number of the workers are employed by Monadelphus and contracted out to projects.

A sign at Searipple Camp advises workers about the bout of gastro. ( Supplied )

Worker Shaun Webster was discharged from hospital after three days, but said he did not want to return to the camp.

"I don't know if anything's been done to inspect or if it's good to go back," he said.

"They want to discharge me today but I'm concerned for my health again going back there."

He believed he became ill after eating food that workers have been fed at the facility.

"When I was first admitted in the emergency ward, I could hear the nurse interviewing the first lot of people [from the camp]. A lot of people said it was poultry-related; pies and eggs came up a fair bit."

ISS Facility Services Australia, which provides hospitality services to Searipple Village, said it had very strict food production controls in place.

In a statement, it said it was aware that approximately 20 out of 820 customers at the village were ill and was taking these reports seriously.

The CFMEU is calling for an inspection of the camp's food, health and safety. ( Supplied )

Mr Webster said he had suffered from gastro before but not like this.

"I've experienced a lot of muscle cramping, tight cramps in the stomach, pains from vomiting so much and diarrhoea at the same time.

"I've had real bad headaches where it's a sharp pain behind your eyes. Hot and cold sweats constantly. I had about six or seven litres of fluid put into me because I was so dehydrated," he said.

Another Monodelphus worker, Simon, said he has been sick for seven days.

He said at the moment he felt like he was on the mend but "36 hours ago that wasn't the case".

"I was up sleepless all night with the shivers and the cold sweats. If you had asked me then how am I feeling, I would have said dying," he said.

He went to hospital but, as he was on the mend, was told to go home rather than risk becoming sicker, and has remained in his small room since.

"It's like being in a prison. I can't go anywhere and I have to provide all my own food so I don't infect anyone else," he said.

Paul Ferreira has asked for casual workers' wages to be covered while they are sick. ( ABC North West WA: Sonia Feng )

Mr Ferreira said the union was concerned some workers may not be entitled to sick leave, or only partial payments.

"Due to the heavy casualisation of the workforce, these workers aren't entitled to sick leave. I have asked Monadelphus that their wages are covered while they are sick."

He also called for a food, health and safety inspection of the camp.

"They [the workers] believe it's food poisoning. I constantly get complaints about the food quality at that camp.

"The first concern is to get these workers fit and healthy to return back to the workforce. They're up here to earn some money."

It is understood authorities met in Karratha on Friday to discuss the outbreak.

The City of Karratha said it was investigating the outbreak, adding that Searipple was subject to routine health and safety inspections.

Comment has been sought from Monadelphus.