Latest figures released by EMAS reveal it has a £8.74m deficit - 20 times higher than predicted.
The NHS Trust Development Authority, which monitors trusts, said it was working closely with the service to help address financial pressures.
EMAS said it has spent more on extra vehicles, staff, training and overtime payments.
It had predicted an overspend of about £500,000 at the start of the year.
The money problems at EMAS are getting worse.
One of the biggest problems is handover delays to A&E because they're too busy to accept patients straight away.
So far this year, more than 10,000 patients have had to wait more than an hour and because the ambulance service gets paid for each patient it takes to hospital, they are losing out.
Also the NHS would like to treat more people at home, but of course it is a financial disincentive.
Our busiest A&E department at Leicester Royal Infirmary is trying to sort it out, but I don't think there's any quick fix.
EMAS claims it is owed £2.6m in compensation for the handover delays, which has contributed to the overspend.
The deficit could rise as demand for the emergency service traditionally increases in January and February.
Richard Wheeler, director of finance of EMAS, said: "The challenges we face come with an increase in cost, including cost of training and upskilling our frontline staff, given the national shortage in paramedics.
"[Also an] increased cost in providing additional staff and vehicles to cover for staff delayed at hospitals, and also extra payments for shifts which don't finish on time.
"Our five-year business plan... will contribute financially and to future sustainability.
"We will not do anything that will impact negatively on patient safety or care," he added.
A spokesperson for the NHS Trust Development Authority said: "It is a challenging time... and [we] are working closely with EMAS to help them address ongoing pressures around finances."
East Midlands Ambulance Service (EMAS) has overspent by almost £9m so far this financial year.