Ecuador opens bidding by private and state companies Wednesday for rights to explore for oil in 16 blocks in the Amazon amid protests from indigenous communities.

Indian protesters clashed with police outside a Quito hotel where government officials were explaining the process to potential bidders.

No injuries were reported, but witnesses said riot police were struck with spears as protesters tried to push their way into the hotel.

"Oil comes out and the land bleeds," protesters shouted.

The auction, which was to be formally launched later in the day by Ecuador's leftist President Rafael Correa, is the OPEC member's first on a large scale since 2002.

The government has opened 13 blocks to bids by private companies, which can form joint ventures with state companies, while three other blocks have been reserved for joint ventures between the Ecuadoran state company Petroamazonas and other state companies.

Altogether, the blocks have potential reserves of 1.6 billion barrels of oil, according to the government.

But the blocks in contention are considered high risk because they are in a 200,000 hectare (500,000 acre) area in the Ecuador's southeastern Amazon that was already previously explored in the 1970s and '80s.

The bidding closes May 30, and contracts are to be signed in September, Non-renewable Resources Minister Wilson Pastor said, adding that Ecuador hopes the auction will bring in $1.0 to 1.2 billion in investments.

Pastor said Petroperu and Ecopetrol, state companies from Peru and Colombia respectively, have expressed interest in the auction.

Venezuela's PDVSA and Enap of Chile have also been mentioned as possible bidders.