Greenpeace said activists on its Arctic Sunrise protest boat sailed to the zone where they expected Spanish oil group Repsol to launch its explorations this weekend, vowing to block the prospecting vessel.
Local groups meanwhile called rallies on Friday right across the Atlantic archipelago, whose beaches are a popular draw for foreign tourists from Britain, France and elsewhere.
Locals and authorities in the Canaries oppose Repsol's government-backed plan to spend three years probing for oil and gas under the sea bed 50 kilometres (30 miles) from the islands of Lanzarote and Fuerteventura.
Residents fear Repsol's explorations will harm local flora and fauna such as dolphins and disrupt the tourism industry on which their economy relies.
They have tried in vain to stop the prospections going ahead.
"It seems that Repsol and the Spanish government still intend to begin the prospection," said Fran Castro, a local spokesman for Ecologists in Action, demonstrating near the port on the island of Tenerife.
"We are going to try and keep up the popular opposition to it until the last moment. We consider this project a catastrophe for the future of the Canaries," he told AFP.
Environmental groups and local councils have complained to EU authorities over Repsol's plan.
The Canary Islands regional government also opposes the plan and has called a referendum to allow residents to vote on it, but the national government has blocked that in the courts.
Repsol has promised to take steps to protect the environment and says the project will create jobs in the islands, where the unemployment rate is over 30 percent.