Colombian authorities have sent 480 police and soldiers to the country's biggest oil field after vandals trashed local offices of its Canadian operater.

The oil field is majority-owned by Toronto-based Pacific Rubiales Energy Corp. and it produces a quarter of Colombia's oil.

Labour unrest has plagued it since July.

The company blamed the oil worker's union for Tuesday's vandalism, but the union denied responsibility.

The firm issued a statement Wednesday from Toronto saying the "disturbances are the result of actions by groups of people who do not work for the company."

"The company has not suspended oil production at the fields, and it intends to do its utmost, in coordination with government security forces, to seek a prompt resolution to these disturbances," the statement said.

Unionized workers are seeking pay raises and better food and living conditions at the 64,000-hectare Rubiales and Quifa fields near Puerto Gaitan on Colombia's eastern plains.

It employs 12,000 and produces 225,000 barrels a day. Labour unrest forced a two-day suspension of operations in August.

With files from The Canadian Press