* Fire alarm raised at Andover site at 0244 GMT
* 20 fire appliances in attendance
* Fire not out yet
* Andover is showcase for Ocado's technology (Updates with firefighters continuing to tackle fire)
LONDON, Feb 5 (Reuters) - Firefighters were tackling a fire at online supermarket pioneer Ocado Group Plc's flagship automated distribution centre in Andover, southern England, more than 18 hours after the alarm was first raised.
A spokesman for Hampshire Fire and Rescue Service said on Tuesday that the service was called at 0244 GMT.
In addition to about 20 fire appliances at the scene, several specialist vehicles helped crews to fight the blaze, he said, adding that no one has suffered injury.
Asked if the warehouse had sustained serious damage, the spokesman said "probably".
The service was continuing to fight fire at the warehouse, a spokeswoman said at 2130 GMT.
Ocado said the fire had broken out on one of its grids of robots and operations had been suspended.
The group, founded by three Goldman Sachs bankers 18 years ago, has nearly doubled its stock market value over the past year after striking deals to sell its technology - showcased in Andover - to other food retailers wanting online delivery.
The company, which on Tuesday reported full-year earnings and cautioned that investment in partnership deals would hit short-term profits, said the fire had affected a proportion of the mechanical handling equipment at the highly automated centre.
"A fire started in a section of the ambient grid of our Andover CFC (customer fulfilment centre). The Fire Brigade is on site. All relevant safety measures were carried out," Ocado said.
"Although some orders had already left the warehouse before the incident and will be delivered as normal, Andover suspended operation this morning, preventing further fulfilment of orders."
The Andover plant, which can process 65,000 orders a week, is Ocado's third automated warehouse - or customer fulfilment centre, as it calls them - and has been instrumental in the firm winning four major overseas partnership deals, including one with U.S. group Kroger Co.
While Ocado's first two CFCs required humans to load thousands of crates travelling on miles of conveyor belts, Andover has hundreds of robots speeding along at four metres per second.
Media reports have said Ocado is in talks with Marks & Spencer about a possible tie-up, but both parties have declined to comment.
Ocado shares closed 4.2 percent up. (Reporting by James Davey and Paul Sandle; editing by David Goodman and Lisa Shumaker)