MADRID (AP) — Authorities in Gibraltar seized 2.6 metric tons of cannabis resin with a street value of 15 million euros ($18 million) after a boat carrying the illicit substance rammed a Customs vessel during a high-speed chase at sea, officials said on Wednesday.

Police spotted the boat off the tiny British territory on Spain’s southern tip and believed it to be suspicious, a Gibraltar government statement said.

A Marine Police vessel attempted to intercept the rigid-hulled inflatable boat, which sped away and began dumping overboard bales of what turned out to be cannabis resin.

A Customs vessel took over the pursuit as the boat's occupants continued to dump bales of the resin. In its attempt to evade arrest, the boat rammed the Customs vessel causing significant damage, the statement said.

Customs officers boarded the vessel and arrested four men.

In all, 65 bales of cannabis resin were seized.