Thailand has begun using sleeper trains to transport Covid patients out of Bangkok, where hospitals have been overwhelmed by a recent surge in cases.

The first train left the capital on Tuesday, transporting 137 patients who were asymptomatic or had mild symptoms to their home towns in the north-east of the country.

Thailand is facing its third and most severe wave of Covid since the start of the pandemic, driven by the Delta variant, which has spread widely across the capital. Hospitals have been forced to treat patients in car parking areas, and to turn away patients who are severely ill.

Since April, the country’s total fatalities have grown from fewer than 100 to 4,397. On Wednesday, 16,533 cases and 133 deaths were reported.

Public health minister Anutin Charnvirakul said on Tuesday the service would move patients who were unable to access treatment in Bangkok. “The process is all secured because they will be closely monitored by doctors and staff and won’t stop anywhere. There will be an emergency team and ambulance standby at the destination,” he said.

Buses, vans and planes may also be used to move people across the country, he said.

A further 15 carriages will be used to isolate patients who are awaiting hospital beds in Bangkok.

A doctor from the group Mor Mai Thon (Doctors Won’t Tolerate It), which has criticised the government response, described the situation in Bangkok as critical. “It has reached the point where people cannot access medical care at all, which has never happened before. There are a huge number of people who can’t get treated,” the doctor, who asked to be anonymous, said.

Moving patients with mild symptoms could help Bangkok’s hospitals in the short term, the doctor said. But they added that if such patients developed more severe illness, this could overwhelm hospitals in other areas of the country, where there are fewer intensive care beds. “The Delta variant is very strong, 50% of the patients develop a severe condition,” they said.

The government should focus on expanding testing capacity, the doctor said, while medicines need to be given more quickly to patients to prevent their illness from deteriorating.

About 70,000 tests are performed each day, with 20.5% returning positive. Demand for testing is so high that long queues stretch outside hospitals where swabs are conducted.

Thailand managed to escape the worst of the virus last year, when it introduced strict lockdown measures, and rolled out test and trace systems. Critics have accused the government of complacency since then, especially in relation to the country’s vaccination campaign, which has suffered from delays and shortages.

About 5% of the Thai population is fully vaccinated, while 12.4% have received one dose, according to Our World in Data. Large crowds have gathered at Bang Sue Grand Station over recent weeks, Bangkok’s vaccination hub, prompting concerns that the virus could spread at the centre.

Mor Mai Thon is calling for greater transparency around the government’s vaccine contracts and for officials to focus on procuring a greater variety of doses.

Thailand is relying on AstraZeneca and Sinovac. However, studies suggest that Sinovac’s efficacy falls 40 days after the second dose. Growing numbers of Thai medics – who were given this vaccine earlier in the year – have become infected. While most medics experience mild illness, they are required to isolate and this places greater pressure on resources.

“When one doctor gets infected, the people surrounding them – such as nurses, medical students – also need to do quarantine,” said Suvinai Jiraboonsri, president of IFMSA, a medical student group. “It’s a waste of time and resources in this critical moment. They need to get better vaccines.”

The government has said it will give booster jabs of alternative doses to medics.