A woman has been arrested after injuring three people in a third knife attack recorded at schools in Poland this week.

The 21-year-old used a "dangerous object" to attack a 17-year-old girl at an educational institution in the capital, Warsaw, police told news agencies PAP and AP.

It comes a day after thousands of police visited schools across Poland, following two stabbing attacks earlier in the week, one of which led to the killing of a female caretaker.

A Warsaw police spokesperson said they could not confirm whether the latest incident was related to the two previous attacks.

Authorities told local media that the 17-year-old injured on Saturday had been taken to hospital, but her condition was not life-threatening.

Two other women aged 17 and 24, who had gone in to submit enrolment documents, were also injured, Poland's state news agency reported.

Police told local media that the suspected attacker was a student at the school and initial findings suggested that she did not know the three victims.

Schools in Poland had been stepping up security following knife attacks at schools across the country on 7 and 8 October. Polish police said they had detained 76 people after deploying to schools across the country.

"When it comes to the safety of Polish children and peace in our schools, there is no room for compromise," Polish Prime Minister Donald Tusk said ahead of the operation.

Local media, citing a police spokesperson, reported authorities had information to suggest incidents this past week could be related to an internet challenge.

On Wednesday, a 19-year-old student attacked and injured nine people at a vocational school in the central Polish province of Mazovian.

A day later, a 37-year-old caretaker was killed after a 15-year-old entered a primary school in Leszczydół-Nowiny, north of Warsaw.

Interior Minister Marcin Kierwiński also said a 17-year-old was detained in the town of Sierpc, north-west of Warsaw, after allegedly stating "on school grounds that he planned to do something... dangerous - that he intended to harm someone".