An American couple carrying swaddled dolls have been caught repeatedly trying to sneak into a maternity ward in California.

Mercy Medical Centre in Merced alerted police and other hospitals in the area after the man and woman were caught on two separate occasions trying to get past security with the dolls.

"They acted like they were real," the hospital's spokesman Robert McLaughlin told ABC News .

"They hold them and hug them and change their diapers. It's very odd."

Staff first spotted the man and woman in the hospital's emergency room on Saturday.

The man was treated for an injury before going up to the second floor where the maternity ward is located.

The woman was wearing hospital scrubs and carrying an outdated business card belonging to the hospital director.

Staff from each floor of the hospital wear different colours so maternity staff recognised immediately that the woman did not work there, Mr McLaughlin said.

When questioned they said they had an appointment with an educator, which turned out not to be true.

The couple returned to the ward on Monday. They were turned away by a security guard on both occasions.

A photo of the pair taken by a security guard suspicious of their intentions helped police to track them down.

They have identified the couple and are investigating, but are not believed to be facing any criminal charges.

"It's not illegal to have a fake baby," Mr McLaughlin said.