Speaking in Brussels, Dombrovskis said that while Europe "remains on the right track", some EU economies were "losing momentum."
He said, "The effects of previous fiscal and structural efforts are by now becoming tangible and substantive. But political risk and reform fatigue are clouds on Europe's horizon.
"Overall, you could sum it up as saying that, on the one hand, governments are showing a somewhat belated sense of urgency while, on the other hand, there are those harbouring a possibly false sense of security."
The Latvian official added, "It must be said that the economic context today is edgy. Yes, the European economy continues to grow moderately but steadily."
In 2015, he said the EU's gross domestic product, GDP, expanded by two per cent and by 1.7 per cent in the Eurozone area, the best performance since 2010. In the first quarter of 2016, GDP expanded by 0.5 per cent in both the euro area and the EU.
"For more than a year," he said, "we had the benefit of a good combination of external and domestic tailwinds and the strength of the expansion exceeds the underlying growth trends."
The former Latvian Prime Minister said that, according to the EU's latest forecasts, published earlier this month, the euro area is expected to grow at 1.6 per cent in this year and 1.8 per cent next year, slightly less than forecasts.
Looking to the future, he said that "hesitant global growth, weak global trade and increased uncertainty look set to weigh more heavily on our prospects than was previously expected."
Addressing an event on economic indicators, organised by the Brussels-based think tank, the Lisbon Council, the commissioner said, "But on the positive side there are still low oil prices and lagged effects from the weak euro exchange rate, even if this is also diminishing in strength."
Turning to the ongoing structural reform process, he said, "For Europe to grow we have only ourselves to depend on. So we need to stay on course. This means: redouble our efforts on implementing structural reforms, keep our budgets under control and attract more investment."
In the speech on Monday, he said, "We need to make more progress on structural reforms across the board.
"Our current assessment is that countries have made between 'limited' and 'some progress' in their implementation.
"I believe this is not good enough."
He went on, "We fully acknowledge that the reform strategy requires political courage to tackle powerful vested interests. Some reforms may bear budgetary costs and others may be technically complex.
"Very often countries also face challenges in terms of their administrative and institutional capacity. Mere legislation is not enough. Effective implementation is what counts."