North Korea appears to be resorting to its old tactic of taking foreigners hostage when things do not go its way, with reports of the arrest of an Australian and a Japanese man in Pyongyang.

Alek Sigley, identified as a 29-year-old Australian student in Pyongyang, has been missing since Monday, ABC reported Wednesday.

And Kenji Fujimoto, the garrulous former sushi chef of former North Korean leader Kim Jong-il, may also have been arrested there, Japanese media reported earlier.

Australian authorities are "urgently seeking clarification" of his fate through the Swedish Embassy in Pyongyang, which serves as a conduit for countries that have no formal diplomatic relations with the North.

Sigley had been studying on a graduate course in Korean literature at Kim Il-sung University since April last year and also runs a company providing guided tours of the North. His latest blog post on Monday showed a photo of the notoriously unfinished Ryugyong Hotel with the caption, "New signage above the main entrance to the Ryugyong Hotel bearing its name and logo. A sign that it will soon be open for business?"

In public statements Sigley has generally talked up conditions in the North, so it is unclear how he could have fallen foul of the regime.

The previous day, the Daily Shincho quoted a security official as saying that Fujimoto, who has often talked out of school about the North Korean regime, is rumored to have been arrested on espionage charges.

The possible arrests come as world leaders gather in Japan for the G20 Summit and Japan and Australia are helping the U.S. with patrol planes and ships to stop illegal ship-to-ship transfers of oil bound for North Korea.

There are fears that the two men could share the fate of Otto Warmbier, an American student who was arrested in the North in 2016 and sent back in a coma from injuries sustained in detention a year later. He died shortly afterwards.

Meanwhile, the North Korean regime is reportedly offering rewards to anyone reporting people who cross into China or exchange phone calls with foreigners.

"The U.S. has recently offered to pay US$5 million as a reward for tip-offs on the regime's violations of the international sanctions," a source said. "This aims to nip in the bud any attempts to claim the U.S. reward."

