Thousands of people have joined a women's protest in Warsaw and other Polish cities, fighting back against the latest attempt by the conservative government to restrict abortion.

In Warsaw, they held banners including "Free choice" and "A woman is a human being" and chanted slogans demanding reproductive freedom.

Poland has one of the strictest abortion laws in Europe, allowed only if the woman's life is at risk, the pregnancy is the result of rape or incest or the foetus is damaged.

An attempt to ban all abortions in 2016 sparked mass nationwide protests by women dressed in black that forced the government to abandon the plan.

The proposed legislation would still allow abortions in cases where the mother's life is at risk or the pregnancy results from a crime.

But it would ban abortions of irreparably sick or impaired foetuses and those with Down's syndrome.

In Warsaw, protesters gathered at the seat of the influential Roman Catholic bishops, who are urging the further tightening of one of Europe's strictest anti-abortion laws.

They then marched to the parliament and later began moving on to the headquarters of the ruling right-wing party housing the office of party leader Jaroslaw Kaczynski.

A protest of hundreds in Wroclaw included a sign that said "I will not give birth to a dead baby."

The European Union's commissioner for human rights Nils Muiznieks and UN experts are urging the parliament to reject the bill.

The proposal was brought by a civic organisation and is now at the commission stage in parliament.