PORTLAND – While the freezing cold is sending some homeless people into shelters, many still try to brave the winter outdoors.

Social workers and police are stepping up their efforts to find homeless people and coax them indoors as temperatures plunge into the teens.

Robert Rockett, a city outreach worker, said the homeless are often afraid of crowds and usually have mental health or substance abuse problems.

There’s no way to know how many homeless people stay outdoors instead of seeking room at shelters, but officials, social service agencies and the homeless themselves say there are more now than there were in recent years. Estimates range from 25 to 50.

Across Maine, 1999 was the third year in a row in which homelessness increased, the Maine State Housing Authority said. Maine’s occupancy rate at shelters rose 21 percent last year, and officials say it was part of a national trend.

Rising rents in the Portland area are a major reason why the city’s homeless shelters are busier this winter.

Those who continue to stay in hidden corners and crannies across Maine’s largest city are exposed to violence and exploitation, in addition to the effects of severe weather conditions.

The homeless are more likely to be assaulted or raped, and are far less likely to report such crimes.

An area known as the Hobo Jungle in Portland’s West End includes a network of well-worn trails linking occupied and abandoned camps.

Some of the homeless have advanced survival skills and are resourceful.

Until recently, Air Force veteran Eric Swenson had been living in a rusting oil tank perched on a heap of scrap metal on the outskirts of downtown Portland.

“I call it the sub,” said Swenson, who used a torch to cut a “hatch” through its wall.

Scrap-yard workers moved it higher on the pile and out of reach, taking away Swenson’s home. He has spent some nights at the city’s Oxford Street Shelter, where more than 100 people stay each night, but says he would rather be outside.