Smoke was seen coming from a Eurotunnel freight service
The operator Eurotunnel said it suspended rail services on Monday afternoon when a fire alarm went off.
Lorry drivers were taken off the train in the north-running tunnel. A fire was put out about 7.5 miles (12km) from Folkestone. No-one was hurt.
Eurostar said passengers were being told to expect "continuing delays".
A spokesman for Eurostar said: "We are advising passengers to avoid travelling today if possible. Tickets can be exchanged for another day."
Eurotunnel's terminals re-opened at about 1700 BST with a limited service in operation.
Two freight shuttles are running every 90 minutes, with delays of up to two hours.
There are also reduced passenger services running every 90 minutes from Folkestone to France.
'Clear backlog'
Eurotunnel spokesman John Keefe said: "It was a freight shuttle going through with about 34 people on board, who have all been evacuated safely."
He added the small fire was extinguished quickly.
"Eurotunnel is conducting checks of the tunnel and its equipment. Once these investigations are completed, Eurotunnel will commence a progressive restart of commercial services," said Mr Keefe
Fire officers from Kent and France extinguished the blaze
"Unfortunately with this being a very busy time of year, it's going to take a few hours to clear the backlog once we've got started again."
A spokesman from Kent Fire and Rescue Service said crews from Folkestone, Deal and Ashford were sent to the scene, along with firefighters based at the tunnel, to help with efforts to reach the freight shuttle.
The 30 passengers and four crew were escorted to the service tunnel.
"Although smoke has been seen there has apparently been no flames and there have been no casualties," he said.
French fire crews also attended the incident.
Traffic using the tunnel was diverted to Dover.
Thirty-four people had to be evacuated this lunchtime after a fire started on a lorry, which was being transported on a freight train in the Channel Tunnel.

Eurotunnel, the operator of the Channel Tunnel, said all services had to be suspended this afternoon due to the small blaze in which nobody was hurt.

John Keefe, a spokesman for Eurotunnel, said: "It was a freight shuttle going through with about 34 people on board, who have all been evacuated safely.

"Eurotunnel is conducting checks of the tunnel and its equipment. Once these investigations are completed, Eurotunnel will commence a progressive restart of commercial services." 

The company also said services through the Tunnel would hopefully 
resume later today. "Unfortunately with this being a very busy time of year, it's going to take a few hours to clear the backlog once we've got started again," said Mr Keefe. 

A Eurostar spokesman said: "We are advising passengers to avoid travelling today if possible. Tickets can be exchanged for another day." 

The Channel Tunnel is a 31 mile long rail tunnel beneath the English Channel which connects Folkestone in Kent to Coquelles near Calais in northern France.