Hawaiian tourism officials are urging visitors to return to the state's Big Island as the Kilauea volcano calms and some gas emissions are the lowest they've been in more than a decade.

The flows - which have expanded the island by the size of 350 rugby fields - deterred thousands of visitors. There was an overall 12.7 per cent slump in tourists in July, although figures from the Hawaii Tourism Oceania show Kiwis bucked the trend, with numbers down by 5.5 per cent for the month.

Overall, New Zealand visits to the Big Island are up 1.1 per cent during the past 12 months.

It has been a month since the continuous flow of lava ceased from Kilauea, and authorities say the clean and clear air quality island-wide was the most evident sign of the positive impact since then.

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The US Geological Survey and Hawaiian Volcano Observatory were also reporting that sulphur dioxide emissions at Kilauea summit and in the Lower East Rift Zone in Puna, where lava flows were occurring, have been drastically reduced and are at their lowest combined level since 2007.

Three weeks ago the alert level for Kilauea volcano was lowered from a warning to a watch level.

Kilauea volcano's latest eruption began on May 3 with lava flowing continuously until August 6. The affected area in lower Puna comprises less than one per cent of the island of Hawaii, which measures 10,400sq km and is larger than all of the other Hawaiian Islands combined.

George D Szigeti, president and chief executive of the Hawaii Tourism Authority, said that after three months of continuous lava flows, he was hopeful this cessation in activity becomes permanent.

"We encourage travellers from around the world to come and enjoy the incredible diversity of landscapes and natural beauty to be explored on the island of Hawaii. The island is safe to visit, the air quality is good and, by coming here, travellers will be supporting community economies and helping residents with their recovery."

About 35sq km of land in the lower Puna area have been covered by lava, with flows into the ocean having added an estimated 354 hectares of new land to the island.

More than 700 homes were destroyed and many businesses have suffered significant losses in revenue, primarily because many visitors have chosen to avoid the area.

Hawaii Volcanoes National Park, the state's most popular visitor attraction, has announced plans to reopen more parts of the park on September 22. Because of damage caused by the volcano activity, most of the park has been closed since early May.