“We will continue this service until no COVID-19 patients who cannot get beds in Bangkok are left,” he said.
He said buses, vans and even aircraft might be deployed to send people back to less badly affected provinces.
Thailand initially kept coronavirus cases in check but outbreaks have flared in recent months.
Prime Minister Prayuth Chan-ocha’s government is facing harsh criticism over its handling of a delta variant-fueled surge and slow vaccination program, amid reports of people dying in the streets or in their homes while waiting for treatment.
Of Thailand's total of nearly 500,000 confirmed cases and more than 4,000 fatalities, 137,263 cases and 2,176 deaths have been recorded in Bangkok.
Most of the 4,451 beds for COVID-19 patients in the city of about 15 million are occupied by people with mild or no symptoms. Hospitals are beginning to urge such patients to isolate at home or in community isolation centers.
Bangkok Gov. Aswin Kwanmuang said the city government will coordinate with the State Railway to install 240 beds in 15 railway carriages in a maintenance shed in the city's huge Bang Sue station as a “pre-admission center" for coronavirus patients without symptoms.
He visited the station on Tuesday to inspect the carriages. He said they should be ready for use by Friday.
The government said supplies of medical oxygen are sufficient and manufacturers have been asked to ensure enough is available. But people ill with coronavirus who are unable to find places for treatment are not always able to get supplemental oxygen.
Meanwhile, some temples in the devoutly Buddhist country have begun to offer free cremations as the number of deaths rises, the government said.