A 28-year-old woman in Germany has admitted killing five of her own newborn infants over several years, police said Thursday, charging her with five counts of manslaughter.

Authorities in the northern city of Flensburg said the woman, who was not named, had confessed to the killing of two babies whose bodies were found in a paper-recycling plant and a car park in March 2006 and March 2007.

During questioning, she then also admitted she had later killed three other newborns, stashing the corpses in her cellar, in previously unknown cases, police and prosecutors said at a joint news conference.

Authorities said autopsies had found no indication of the cause or exact timing of the deaths.

"It is important to stress that no one else was involved in these acts," police spokesman Dirk Czarnetzki told reporters.

"No one knew about the pregnancies or the birth of these children," he added.

The woman, who is now in custody, is married with two children aged eight and 10.

Her husband did not wish to expand their family, prosecutor Ulrike Stahlmann-Liebelt said.

"She was worried that he would leave her if he found out about (the other births) because he did not want to have any more children," Stahlmann-Liebelt said. "She felt she had nowhere else to turn.

"She had not seriously considered contraception and had not been to the gynaecologist in recent years," added the prosecutor.

The husband, who is receiving counselling, was described as "completely devastated". He told police he knew nothing about the pregnancies.

The suspect managed to conceal her condition "by being withdrawn and wearing loose clothing," the prosecutor added. "Two of the children were born at home, the other three in the woods."

Stahlmann-Liebelt said the investigation was at a preliminary stage and she could not speculate on a possible sentence.

Authorities said they had carried out saliva tests on "hundreds of women in the area" after the two bodies were discovered in 2006 and 2007.

The suspect was asked to offer a saliva test on Tuesday and handed herself in shortly afterwards, Czarnetzki said.

The family was completely "unremarkable" and had not come to the attention of social services.

Infanticide is not an uncommon crime in Germany and several high-profile cases have made headlines this year already.

In March, a 33-year-old woman was sentenced to 13 years behind bars after being convicted of killing her three babies shortly after birth.

Police are also investigating the mother of three babies found dead in April, who says they were stillborn.

The case announced on Thursday was however thought to be the worst to come to light in Germany since 2005, when a mother was sentenced to 15 years in prison after killing eight of her newborns.

In that case, the corpses were discovered in buckets and flower pots during a garage clear-out at the home the woman shared with her husband, and in an old fish tank at the home of her parents.

She was also accused of killing a ninth baby, born in 1988, but the court ruled that the time in which she could be charged in connection with that death had lapsed.