Eko Hot Blog reports that people had been playing on the ice at Babbs Mill Park and fell through, according to West Midlands Fire Service.
It said people had received treatment before being taken to the hospital.
Specialist teams and equipment are involved in the search.
The fire service said they were called shortly after 14:30 GMT on Sunday.
Concerned members of the community gathered near the scene in what is a residential area, as emergency services carried out work at the lake.
A drone was also spotted flying over the water.
It was likely that the emergency service presence would remain there for several hours.
Local MP Saqib Bhatti said he was being kept updated on the situation, adding in a tweet: “My thoughts and prayers are with the whole community and I pray for all those that are affected.”
Babbs Mill Park is a local nature reserve with a lake, river, wildflower grasslands, and woodlands.
Temperatures of 1C (34F) were reported in the area at the time the emergency services were called. They are expected to plummet to -3C during the night.
Meanwhile, police in Cumbria said they were dealing with an “incident” at Siddick Pond in Workington. The force later confirmed no one was unaccounted for.
The Met Office warned of the dangers posed by ice.
A spokesperson said: “With temperatures set to struggle to get much above freezing over the coming days across much of the country, stretches of water such as rivers and ponds are at risk of freezing.
“While frozen rivers and ponds can be fascinating, they can be dangerous and a hazard to life.”
Source: BBC
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