Gurria told Lusa News Agency in an interview during a break at the presentation of the OECD's new report in Lisbon that what determined the number of children a family had was their future perspective.

He added that low birth rates happened in countries with higher standards of living, whether these are "Buddhist, Catholic or Protestant."

He also said problems relating to access to housing, namely for young people, were crucial, adding that there was a "problem" regarding young people's confidence in the future.

New generations don't believe they will be as well off as their parents, he explained. "At the moment, we have a crisis of expectations," Gurría went on.

Gurría also pointed out that the quality of nurseries was another determining factor, which he said had a "magic effect" in all countries around the world.

But it is also necessary to create a "generation of professionals," he noted.

Latest figures released by the EU's statistics body Eurostat showed that Portugal's fertility index sat at 1.36 births per women in 2016, below the average of the 35 OECD member states of 1.65 children, and below the 28-country European Union of 1.60 children.

Regarding Portugal's pension system problem, Gurría said this was a "general problem" and that it was necessary to prolong working years as people's lives are getting longer.

The OECD said in its latest report - presented on Monday in Lisbon by OECD secretary-general Angel Gurría alongside Siza Vieira and deputy minister and secretary of state of finance Ricardo Mourinho Félix - that Portugal had too many tax exemptions and reduced rates, in particular for VAT.

According to the report, Portugal’s economic recovery is "well established," with GDP "back to pre-crisis levels, a substantially lower unemployment rate and renewed investment and domestic consumption now joining a robust export sector to drive the economy."

The organisation also said the country needs to "focus on reducing vulnerabilities to build resilience to future shocks."