A statement issued by the Welsh Government said the move would "mean local authorities can use leisure centres as temporary hospitals if they are needed to prevent or control an emergency".
It added that, under the permitted rights, "any temporary structures must be removed and the land restored to its previous condition (or to an agreed condition) within 12 months of the development starting".
Alternatively, it added, "planning permission would have to be sought for any continuing use".
Regulations to enact the change came into effect on Monday (30 March).
Welsh housing and local government minister Julie James said: "Local authorities in Wales are doing an excellent job of responding to rapidly changing situations and it is vital that we allow them to meet their wide-ranging responsibilities quickly.
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"Relaxing the usual planning requirements allows local authorities to take swift action to respond to local need."
Separately, the Welsh Government has issued guidance on how the planning system should operate during the pandemic.
The document says that the Welsh Government is "looking at whether the bespoke aspects of planning committees need to be amended".
It says that regulations "are likely to come forward using the powers set out in the Coronovirus Act 2020". This allows councils to hold 'virtual' committee meetings and grants devolved administrations powers to implement such changes.
The guidance also says that developers "are unable to fulfil a number of the requirements of the pre-application process" and the Welsh Government is "considering temporary amendments to the Town and Country Planning (Development Management Procedure) (Wales) Order 2012 (DMPWO) to remove the need for site notices and making information available for inspection at a location in the vicinity of the proposed development".
It adds that "similar changes will be considered for Developments of National Significance" and legislation to enact the changes will be brought forward "as soon as possible".