Rescue ships scrambled to save a stricken chemical tanker adrift off France's Atlantic coast after a collision with a freighter forced its crew to abandon ship, maritime officials said.

A deepwater tug was towing the badly listing 120-metre Maltese-flagged Uranus to the port of Brest in France's northwest after a salvage team boarded the ship, which is carrying 6,000 tonnes of solvents.

The ship's 13-member crew, believed to be Turks, took to the life rafts shortly before dawn from where they were winched to safety by rescue helicopter, said the coastguard headquarters in the Brittany city of Brest.

The Uranus was said to be "taking on large amounts of water" after colliding with a bulk carrier 50 nautical miles southwest of the island of Ouessant.

The coastguard later said that they had started to pump water out of the ship, with no pollution visible.

"The salvage team on-board are confident that while the vessel has a 12 degree list to port, there is no immediate danger," the ship's Glasgow-based operator V Ships said, adding that the ship was no longer taking on water.

The ship is carrying heavy pygas, V Ships said in a statement, an industrial gasoline used to make products including paint.

The French transport ministry said the cargo was highly flammable and that the boat was expected to arrive in Brest in the late afternoon.

"We're in more of a favourable situation than an unfavourable one," maritime authority spokesman Marc Gander told journalists in Brest.

The Uranus was built in 2008 and is compartmentalised with a double hull, Gander said, reducing the risk of the solvents leaking into the sea.

"The convoy will be travelling at four knots, which means that it'll take 12 to 13 hours" to reach Brest, Gander said in the morning.

The Uranus was en route from Porto Marghera in Italy to Amsterdam when the collision occurred with the Hanjin Richzad, a 191-metre Panama-flagged freighter travelling from Las Palmas in Spain to Rotterdam in the Netherlands.

One was apparently overtaking the other, Gander said.

The transport ministry said that the collision happened at around 0315 GMT, after which the cargo ship waited to provide help if necessary to the tanker. The Hanjin Richzad was allowed to continue its voyage after being inspected.

Weather at the time of the accident was clement, with a 1.50 metre (five foot) swell, the coastguard said.

The French Regional Operational Centre for Monitoring and Rescue (CROSS) dispatched a navy frigate and the tug to the area.

The Brittany coast is at the western entrance to the Channel, one of the world's busiest waterways, and has in the past been hit by several environmental disasters linked to shipping.

In 1978, the sinking of Liberian-flagged supertanker the Amoco Cadiz devastated around 320 kilometres of pristine shoreline with 230,000 tonnes of crude oil.

In 1999, the Erika tanker, another Maltese-flagged ship, carrying 30,000 tonnes of heavy fuel oil broke in two and sank off Brittany, polluting a large stretch of coastline and killing tens of thousands of seabirds.

The French oil company Total was found guilty of failing to address maintenance problems when it chartered the rusty 25-year-old Erika.

French beach resorts were deserted, fishing was halted and shellfish banned from consumption in the aftermath of the oil spill, leaving the local economy on its knees for years.