Visitors who arrive by air under the Test & Go programme, which resumes on Tuesday, will have to book hotel accommodation twice for two Covid-19 tests.
Taweesilp Visanuyothin of the Centre for Covid-19 Situation Administration said the revised Test & Go scheme now required two Covid-19 tests for each visitor, the first on arrival and second on day 5 of their visit.
Visitors would have to show evidence of bookings for the two nights at a hotel linked with partner hospitals, he said.
"If they test negative in the first test, they can travel freely until the second test," Dr Taweesilp said.
The revised, reopened Test & Go will be available for visitors from all countries, he said.
If their Covid-19 insurance coverage was limited, visitors found to be infected would still have to meet all costs themselves for treatment at hospitals or quarantine hotels, and for disease control responses for high-risk contacts, he said.
Registration for Test & Go entry was suspended late last month due to the spread of the Omicron variant.
This month, Dr Taweesilp said, 22 Test & Go visitors violated disease controls and most could not be located when their Covid-19 tests returned positive.
Violators could face a fine of up to 20,000 baht.