Police in Germany, Austria and Hungary have urged parents to carefully check sweets collected by their children over Halloween after needles and other sharp metal objects were found hidden inside candy handed out to trick-or-treaters.

Cases have been reported in a number of German states, stretching from Bavaria in the south-east to Lower Saxony in the north. In one incident in Bremervörde, west of Hamburg, a nine-year-old girl injured her tongue while eating a chocolate bar, and a pin measuring 5cm (2in) was subsequently discovered inside it.

In Hungary, authorities have opened a criminal investigation after nails, screws and pieces of wire turned up in sweets given to children trick-or-treating in and around the town of Gyömrő, east of Budapest. The local authority said one young girl received a toffee containing a nail wrapped inside a chocolate wrapper, but fortunately spotted the object in time and did not swallow the sweet.

Austria has also seen several reported cases. Interior Minister Gerhard Karner denounced the incidents as "cowardly, malicious and in some cases life-threatening". Police said investigations were under way in four states, and confirmed that a 10-year-old girl suffered a minor injury to her mouth after biting into a small chocolate bar in the Amstetten area, east of Linz.

Lower Austria Governor Johanna Mikl-Leitner said those responsible had to feel the full force of the law, adding: "Our children deserve a carefree childhood and we'll continue to ensure that."

In the south-eastern German state of Bavaria, police said that while similar cases had been recorded over the past two years, early figures suggested a significant rise in incidents this year. As many as 25 cases involving sweets containing needles, screws or nails have been reported by police in the state.

Officers in the Middle Franconia region of western Bavaria also cautioned against the danger of copycat incidents. Their warning followed a case in which a mother reported finding a needle in her child's chocolate bar, only to return to police later and say her child had admitted to inserting the needle.

Authorities across the three countries continue to investigate, and parents have been advised to examine all Halloween treats before allowing children to eat them.