London — An explosion on a truck deep inside the Channel Tunnel yesterday afternoon caused a major fire that nearly turned to disaster.

As fire crews from both sides of the Channel fought the blaze hours after it began, officials disclosed that another vehicle on the train was carrying highly flammable carbolic acid.

All services through the tunnel were suspended while an urgent safety review was carried out, and no trains are expected to run through it until at least lunchtime Friday.

A total of 32 people, many of them British truck drivers, were evacuated from the freight train via a service tunnel as the fire spread to two other vehicles. Six people were treated for smoke inhalation and another eight suffered minor injuries in the scramble to escape.

French officials said the southbound tunnel, where the fire broke out at 2:55 p.m., suffered extensive damage to its walls and safety equipment as temperatures reached 1,832 degrees Fahrenheit.

As an investigation began, it became clear how close the tunnel came to the worst disaster in its 14-year history.

An overheating brake on a truck caused a tire to explode when the train was six miles from the French end of the tunnel. This in turn set fire to the cab. Had the blaze spread to a nearby truck carrying the carbolic acid, the consequences would certainly have been worse than the 1996 fire that closed the tunnel for weeks.

The blaze left hundreds of travelers stranded in France overnight, with others in Britain having to cancel weekend breaks to the Continent.

A French police spokesman said: “It is a very serious fire. The truck caught light with disastrous consequences. All of the tunnels have been shut. There will no more services for the foreseeable future.”

The director of the Pas de Calais region prefect’s office, Francois Malhanche, said there were 30 trucks on the shuttle, including one transporting the carbolic acid, or phenol, which is used in medicines and as an antiseptic. Fire crews are understood to have hosed down the truck carrying phenol during the incident to prevent the chemical vaporizing and exploding.

Phenol is highly flammable and causes potentially deadly burns if it comes into contact with skin.

Nicholas Comfort, the author of a book on the tunnel, said investigators were likely to question whether toxic or flammable liquids should be allowed through the tunnel at all.

“Strict rules have been applied to the carriage of flammable liquids in bulk since the start,” he said. “They were reviewed after the 1996 fire by the Inter-Governmental Safety Commission and supposed to have been more strictly enforced.

“While lorries have diesel in the tank, which is flammable, they should not be part of their cargo.”