The Tewae Siassi District of the Seventh-day Adventist Church is a growing spiritual district in Morobe , encompassing Umboi Island, Siassi, and mainland Tewae, divided by the scenic Vitiaz Strait. 

From Lae, the district lies to the northeast, across the Huon Gulf and the Vitiaz Strait, with Sialum approximately 90–100 kilometers from Lae as the crow flies. The Siassi Islands, including Umboi, are further offshore, about 50–60 kilometers northeast of Sialum across the strait.

In a region historically dominated by Lutheran and Catholic churches, the Seventh-day Adventist Church in Tewae Siassi is steadily expanding, sharing a message of hope and faith with local communities.

Rooted in the Seventh-day Adventist mission, the district is committed to spreading the love of Jesus Christ through worship, service, and fellowship. It promotes spiritual growth, holistic living, and community connection through its churches, which offer inspiring worship services, Bible study groups, youth programs, and outreach initiatives. These efforts address both the spiritual and practical needs of the people. From the serene shores of Umboi Island to the vibrant mainland Tewae, the district unites across the Vitiaz Strait to create a welcoming environment for all to experience God’s grace.T

Number of Organized Church

Yangla Church was the first church in the District to be organised by Morobe Mission in 2017.

Yangla Adventist church has five company churches in Umboi Island,Siassi. The churches are:

1. Aromot                                      Aromot village

2. Ayau Mararamu.                      Mararamu village 

3. Gomlongon                              Gomlongon 

4. Kampalap                                 Kampalap 

5. Ovongai                                    Ovongai