OKLAHOMA CITY, May 10 (Reuters) - At least 16 people were killed on Saturday in Missouri and Oklahoma after tornadoes swept through the area, authorities in the two states said.

A swarm of tornadoes that struck southwest Missouri killed 10 people, Missouri Emergency Management spokeswoman Susie Stonner said.

"Communication to the area, which is mostly rural, is really bad. There are a lot of power outages. There may be additional deaths," she said.

Six people were also killed in the small northeastern Oklahoma town of Picher, officials said.

"Basically a 24-block area is virtually destroyed," said Michelann Ooten, a spokeswoman for the Oklahoma Department of Emergency Management.

She added that Oklahoma Gov. Brad Henry had ordered National Guard troops to arrive in Picher by Sunday morning to help in rescue and recovery operations.

Picher is at the center of a massive federal clean-up of pollution from lead and zinc mining. Residents were being assisted with relocation from the community after high levels of lead were found in groundwater.

Most of the victims in Missouri were in Newton County in the southwestern part of the state near the Oklahoma border, Stonner said.

Hail the size of golf balls fell across parts of the region, and high winds damaged power lines. Trees were uprooted, and trucks blown over, the National Weather Service said.

"There appears to have been one large storm. How many tornadoes, we're trying to sort out now," said NWS meteorologist Ryan Kardell. (Reporting by Ben Fenwick in Oklahoma City; additional reporting by Erwin Seba in Houston and Andrew Stern in Chicago; Editing by Eric Beech)

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