Fire service at the scene of a suspected chemical spill at Palmerston North Hospital.

Palmerston North Hospital's main entrance was cordoned off after an unidentified chemical was brought to the front doors by contaminated workers.

Fire service assistant area commander Rodger Calder said three workers had reported feeling a "burning" sensation before driving themselves to hospital about 3.30pm on Monday.

They had been working on a transformer board that was removed in Kimbolton when they contaminated their clothing with an unidentified chemical, he said.

Calder said the men had driven themselves to hospital, leaving the board in the back of the ute, after they started to have a reaction to the chemical.

No one was evacuated from the hospital but the three workers were admitted to the emergency department with some form of chemical contamination.

Calder said firefighters ensured the area was safe before they flushed out the area and decontaminated their staff.

A MidCentral District Health Board spokesman said the three people had been treated for minor to moderate injuries following normal hospital procedure.

The fire service were called to handle the vehicle that contained the chemical contamination, which required a portion of the carpark to be cordoned off.

The hospital continued to operate as normal and the carpark reopened a few hours after the incident.

Two vehicles were contaminated with the chemical and Crash Services was called in to tow them away for decontamination.

Treena Hardman said she had been on the fourth floor of the hospital visiting her son when she saw the commotion from upstairs.

"We saw everyone crowded around the window looking down. Four guys in hazmat suits all around a white [vehicle].

"They went into the carpark and picked something up and put it in a bucket.

"Then they went hosing down the carpark with a fire hose."

Hardman said when they tried to get information not a lot of people seemed to know what was going on.

"The nurses didn't even know what was going on.

"We asked [the] security guard and she said she couldn't tell us, we weren't allowed to know."

Hardman said her car was still in the carpark as they had not been able to access it when she was leaving.

"It's a paid carpark so I'm hoping [they] don't ping everyone for it.

"I'll just be taking my receipt out and saying I'm not paying that."