Live images show a bus burst into flames after it caught fire in Yizhang county of Hunan province on June 26, 2016.[Photo/Weibo]

A State Council investigative team has identified 42 people responsible for a tour bus fire that killed dozens, an official with the team said on Friday.

The bus was carrying 57 people when it crashed into the guardrail on a highway in Hunan province and went up in flames on June 26.

An oil leak caused the blaze, which killed 35 people, the official said.

Following the team's findings, 21 people have been placed under criminal investigation, while 21 local officials, including a deputy mayor, have received disciplinary and administrative penalties.

The bus driver, identified as Liu Dahui, stands accused of driving while overly fatigued and being directly responsible for the accident, according to the official, who added Liu had not slept for days and lost control of the vehicle.

It was found that the bus door could not open wide enough after the crash, and emergency hammers to break the windows were not accessible to the trapped passengers, mostly tourists.

Chaos set in as Liu and the tour guide escaped from the bus through the window next to the driver's seat without trying to help the trapped passengers escape, the official said.

Thirteen additional people escaped with injuries.

The investigative team called the accident an "extremely serious work safety accident".

The State Council defines "extremely serious" accidents as those that kill more than 30 people, seriously injure 100, or result in over 100million yuan in direct economic losses.

China has vowed to optimize supervision and laws and regulations to reduce work accidents by 2020.

In 2015, there were 38 extremely serious or serious accidents, with almost 300 casualties, data showed.