Indian labourers on construction sites in Qatar have been forced to go without meals, complete 15-hour days in searing temperatures and have been denied medical aid, recently-returned workers have told the Guardian.

Workers who had returned from one construction site in Qatar's capital Doha on Friday described living 20 to a room in filthy conditions and being given enough money to buy only one frugal meal a day, which they ate in a single 15-minute break. They described limited safety equipment or training, and one described having his pay docked for four days spent lying sick in his bed after contracting a stomach infection and said the company he was working for refused to pay for a doctor.

Many say they were promised skilled work as electricians or plumbers by agents but ended up as simple labourers and were not paid.

Vishnu Tatikonda, a 33-year-old electrician from Karimnagar district in the central Indian state of Andhra Pradesh, said he paid 65,000 INR (£645) to an agent in India for a visa, tickets and a placement with a subcontractor for a major construction firm in Qatar who would pay him a monthly salary of 1,200 QAR (£205). However, he instead found himself carrying cement and bricks on a project building 20-floor apartment blocks.

"We had to be ready at 4 every morning to leave for work and we would be dropped back at the room at 9 every night. It was over 50 degrees and in that heat we were surviving on one meal a day. An Indian manager would come to give us 100 riyal (£17) every 15 days for food. I was spending about 10 riyals (£1.70) for one meal. If I wanted to have breakfast, lunch and dinner, it was impossible," Tatikonda said.

The men got 15 minutes off at midday. When the food allowance ran out, Tatikonda said he would make rough Indian flat breads and eat them with curd.

"At times the food would go bad, as I had to pack it before leaving at 4 in the morning, and I would go without even my one meal a day. I had no identity documents or card so I could not go anywhere. They gave me no insurance either. So if I got buried under at the construction site, my family had no security," he said.

When his grandmother died in India, the company paid for a flight home and he left, but was still owed three months' pay.

Udaya Posanna, a 38-year-old plumber from Nizamabad district, Andhra Pradesh, also paid an agent and was sent to Qatar. He also worked for three months without pay.

Promised work as a plumber, he ended up on a 22-floor residential building where he cleaned tiles and carried rubbish.

Posanna was given a cot in "a tiny room with no ventilation or coolers in 50 degrees of heat with 20 other men sleeping there" in the town of Al Khor, 30 miles north of Doha.

"It was a kind of makeshift plywood camp. There were about 60 workers in all – from Andhra Pradesh, Uttar Pradesh [the northern Indian state] and Nepal living in those makeshift plywood rooms. We were given cots that were old and some broken, infested with bed bugs," Posanna said.

When Posanna fell sick the company refused to take him to a doctor or pay for medicine, he said.

"They said we'll give a month's pay after three months of work. I refused that and said I wanted to go back home. The company paid for my ticket to India and gave me 100 riyals (£17) at the airport. They had promised to pay 900 riyals (£153) per month."

The arrangements are in breach of local regulations that set high standards for workers' housing, allowing companies to house no more than four workers in the same room, banning the use of bunk beds, and requiring employers to ensure potable water, air conditioning, and proper ventilation in all worker accommodations.

Hundreds of thousands of Indians work in Qatar, where 1.2 million migrants are employed. The Indian ambassador in Qatar said 82 Indian workers died in the first five months of this year and 1,460 complained to the embassy about labour conditions and consular problems. More than 700 Indian workers died in Qatar between 2010 and 2012.

It is estimated that Qatar, which is the world's richest country by income per capita, is spending the equivalent of £62bn from its gas and oil wealth on building transport infrastructure, hotels, stadiums and other facilities ahead of the World Cup.

According to a report by Human Rights Watch, the campaign group, published last year the abuses described by Posanna and Tatikonda are systematic.