PARIS—The world’s economy is ensnared in weak growth and vulnerable to falling into another deep downturn unless governments take urgent action, the Organization for Economic Cooperation and Development said Wednesday.

Releasing its semiannual economic outlook, the Paris-based organization amplified its call for governments to stimulate their economies by expanding investment and implementing policies that fuel competition, increase labor mobility and strengthen financial stability.

“The need is urgent,” OECD chief economist Catherine Mann said. “The longer the global economy remains in the low-growth trap, the more difficult it will be to break the negative feedback loops,” she added.

The OECD called on governments in February to head off risks to the global economy by ramping up investment spending. The starker warning in the May economic outlook indicates little effective action has been taken and highlights the further dwindling of prospects for more sturdy growth.

In the most recent sign of reluctance among major economies to embark on fiscal stimulus, the Group of Seven leading industrialized nations stopped short of announcing coordinated action at a meeting last week.