TOKYO — Workers’ struggle to plug a gush of highly contaminated water from the Fukushima Daiichi nuclear power station, using sawdust, shredded newspaper and an absorbent powder, appeared to be failing early Monday as the radiation threat from the crippled plant continued to spread.

Water with high amounts of radioactive iodine has been spewing directly into the Pacific Ocean from a large crack discovered Saturday in a six-foot-deep pit at the coastal plant north of Tokyo. The pit is next to the seawater intake pipes at the No. 2 reactor.

After an unsuccessful attempt to flood the pit with concrete to stop the leak, workers on Sunday turned to trying to plug the apparent source of the water — an underground shaft thought to lead to the damaged reactor building — with more than 120 pounds of sawdust, three garbage bags full of shredded newspaper and about nine pounds of a polymeric powder that officials said absorbed 50 times its volume of water.

Although the stopgap measure did not appear to be succeeding, workers would keep trying to stem the leak, said Hidehiko Nishiyama, deputy director general of the Nuclear and Industrial Safety Agency.